Distributed fiber raman temperature sensing apparatus and method based on chaotic multi-pulse coding

Abstract

The present application relates to the field of distributed optical fiber sensing, and discloses a kind of distributed optical fiber Raman sensing device and method based on chaotic multi-pulse coding.The device includes chaotic light source, pulse light modulator is modulated into multiple different multi-pulse sequence optical signals according to coded pulse sequence continuous chaotic laser emitted by the chaotic light source, after being amplified by optical amplifier, the multi-pulse sequence optical signals are divided into two beams by optical splitter, one of which is detected as reference light by the first photoelectric detector, and the other is detected as probe light after passing through wavelength division multiplexer into sensing optical fiber, the chaotic Raman backscattering signal generated is detected by the second photoelectric detector after passing through wavelength division multiplexer;Computer is used to locate and demodulate the temperature abrupt point information along the optical fiber according to the output signals of the first photoelectric detector and the second photoelectric detector under multiple different multi-pulse sequence optical signals.The present application can improve the signal-to-noise ratio, temperature accuracy and sensing distance of the system.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of distributed optical fiber sensing, in particular to a distributed optical fiber Raman sensing device and method based on chaotic multi-pulse coding. BACKGROUND

[0002] The distributed optical fiber Raman sensing system can continuously measure the distributed temperature characteristic information along the sensing optical fiber. In the distributed optical fiber Raman sensing system, the ambient temperature along the sensing optical fiber can modulate the intensity of the Raman scattered light in the optical fiber, and the system can obtain the distributed temperature information along the sensing optical fiber by collecting the Raman scattered light carrying the temperature information. The distributed optical fiber Raman sensing system has the advantages of strong environmental adaptability, anti-electromagnetic interference, large detection range, high temperature precision, etc., and is widely used in temperature safety monitoring fields such as coal mines, oil and gas pipelines, bridges, buildings, etc.

[0003] In the distributed optical fiber Raman sensing system, the spatial resolution is an extremely important technical index, which reflects the minimum length that can distinguish the temperature change of the optical fiber. The probe signal used in the system is a pulse signal, and the positioning principle is the pulse time flight method. The Raman backscattered Stokes signal collected by this method is not the light intensity information of the sensing optical fiber L position point, but the superposition of the light intensity information on a section of the sensing optical fiber with a pulse width of half. This makes the spatial resolution of the traditional distributed Raman sensing system limited by the pulse width. Reducing the pulse width can optimize the spatial resolution of the system, but will worsen the signal-to-noise ratio and sensing distance of the system, which leads to the technical bottleneck that the existing distributed optical fiber Raman sensing system cannot balance the spatial resolution and spatial resolution.

[0004] Therefore, it is necessary to invent a new temperature demodulation method to solve the technical bottleneck that the spatial resolution of the existing distributed optical fiber Raman sensing system is limited by the OTDR principle, which leads to the technical bottleneck that the sensing distance and spatial resolution cannot be balanced, and to improve the signal-to-noise ratio. SUMMARY

[0005] In order to solve the technical bottleneck that the spatial resolution of the existing distributed optical fiber Raman sensing system is limited by the OTDR principle, which leads to the technical bottleneck that the sensing distance and spatial resolution cannot be balanced, and to improve the signal-to-noise ratio, the present application proposes a distributed optical fiber Raman sensing device and method based on chaotic multi-pulse coding, which aims to accurately identify and demodulate the temperature mutation point information along the optical fiber, and finally realize the millimeter-level spatial resolution and high signal-to-noise ratio measurement along the optical fiber.

[0006] To solve the above technical problems, the technical scheme adopted by the present application is: a distributed optical fiber Raman sensing device based on chaotic multi-pulse coding, comprising: a chaotic light source, a pulse light modulator, an optical amplifier, a beam splitter, a first photodetector, a wavelength division multiplexer, a sensing optical fiber, a second photodetector, a data acquisition card, and a computer.

[0007] The pulse light modulator is used to modulate the continuous chaotic laser emitted by the chaotic light source into a plurality of different multi-pulse sequence optical signals according to the coded pulse sequence, and the multi-pulse sequence optical signals are amplified by the optical amplifier and then split into two beams by the beam splitter, one of which is detected by the first photodetector as reference light, and the other is detected by the second photodetector as probe light after passing through the a and b ports of the wavelength division multiplexer and entering the sensing optical fiber, and the chaotic Raman backscattering signal generated in the sensing optical fiber is detected by the second photodetector after passing through the b and c ports of the wavelength division multiplexer; the output signals of the first and second photodetectors are collected by the data acquisition card and then sent to the computer; the coded pulse sequence is a binary symbol array, the total length of the sequence is 2n, and the number of pulses contained in each coded pulse sequence is m.

[0008] The computer is used to calculate the output signals of the first and second photodetectors under the condition of the different multi-pulse sequence optical signals output by the pulse light modulator, and then locate and demodulate the temperature abrupt point information along the optical fiber.

[0009] The chaotic light source comprises a semiconductor laser, a circulator, a beam splitter, a polarization controller, and an optical attenuator, the laser emitted by the semiconductor laser is split into two beams by the beam splitter after passing through the circulator, one of which is returned to the semiconductor laser as feedback light after passing through the polarization controller, the optical attenuator, and the circulator to make the semiconductor laser output chaotic light, and the other is output as the chaotic light source.

[0010] The distributed optical fiber Raman sensing device based on chaotic multi-pulse coding further comprises an optical isolator, which is arranged at the output port of the chaotic light source.

[0011] The wavelength of the chaotic light source is 1550 nm, the wavelength of the a port of the wavelength division multiplexer is 1550 nm, the wavelength of the b port is 1550 nm / 1450 nm, and the wavelength of the c port is 1450 nm.

[0012] The distributed optical fiber Raman sensing device based on chaotic multi-pulse coding further comprises a pulse signal generator, which is used to emit a plurality of different coded pulse sequences to drive the pulse light modulator.

[0013] The specific method for the computer to locate and demodulate the temperature abrupt point information along the optical fiber is:

[0014] ​S101, time-domain differential signal reconstruction is performed on the chaotic Raman back anti-Stokes scattering signal to obtain a chaotic reconstructed Raman back anti-Stokes scattering signal in a short scale;

[0015] S102, short-scale time-domain correlation compression operation is performed on the chaotic pulse sequence reference signal and the reconstructed chaotic Raman back anti-Stokes scattering signal to obtain a short-scale time-domain correlation compression coefficient;

[0016] S103, then, short-scale time-domain correlation compression coefficients under all different multi-pulse encoding sequence signals are summed to obtain a summed short-scale time-domain correlation compression coefficient;

[0017] S104, according to the number of delay sampling points a0 and a1 corresponding to the positive peak value and the negative peak value of the summed short-scale time-domain correlation compression coefficient respectively, and the positive peak value of the summed short-scale time-domain correlation compression coefficient, a temperature mutation position L1, a temperature mutation region length ΔL and temperature information T at the temperature change are calculated; the calculation formula is:

[0018]

[0019] ΔL = (a1-a0)·c / (2n0·f s );

[0020]

[0021] wherein c represents the speed of light, n0 represents the refractive index in the optical fiber, f s represents the sampling rate, h is the Planck constant, Δν is the Raman shift, k is the Boltzmann constant, T0 represents the temperature of the non-temperature change region sensing optical fiber, represents the additional loss information at the temperature change position L1, is the attenuation information at the sensing optical fiber L1, C peak represents the positive peak value of the summed short-scale time-domain correlation compression coefficient, P represents the total power of a single group of pulse sequences, K a represents a coefficient related to the Raman back anti-Stokes scattering cross section, λ a is the wavelength of the Raman back anti-Stokes scattering signal, and A represents the influence function of the temperature mutation region length on the positive correlation peak value.

[0022] The calculation formula of the influence function A of the temperature mutation region length on the positive correlation peak value is:

[0023]

[0024] wherein P j represents the power of the jth data point, and w represents the pulse element width; Q irepresents the value of the i-th symbol in the coded pulse sequence; Δm represents the length of the temperature jump region in the time scale;

[0025] The calculation formula of the decay information and the additional loss information at the temperature change position L1 is:

[0026]

[0027]

[0028] wherein R as (T0) represents the temperature modulation function of the Raman back anti-Stokes scattering light, and P0 represents the power of a single pulse.

[0029] In the S101, the calculation formula of the reconstruction is:

[0030]

[0031] wherein F as (L, j) is the reconstructed chaotic Raman back anti-Stokes scattering signal of the j-th sampling point at the position L; and I as (L) represents the position and the chaotic Raman back anti-Stokes scattering signal at the position L;

[0032] In the S102, the calculation formula of the short-scale time-domain correlation compression coefficient is:

[0033]

[0034] wherein C(a) represents the short-scale time-domain correlation compression coefficient, M represents the total sampling point number of the reconstructed chaotic Raman back anti-Stokes scattering signal, F as (j) represents the reconstructed chaotic Raman back anti-Stokes scattering signal of the j-th sampling point, I ref (i, j+a) represents the chaotic pulse reference signal of the pulse sequence corresponding to the i-th symbol with a sampling point delay a.

[0035] Preferably, m=n.

[0036] Furthermore, the application also provides a distributed optical fiber Raman sensing method based on chaotic multi-pulse coding, and the device used in the method comprises a continuous chaotic laser, a pulse light modulator, a beam splitter, a wavelength division multiplexer, a sensing optical fiber, a first photoelectric detector and a second photoelectric detector, continuous chaotic laser output by the continuous chaotic laser is modulated into a multi-pulse coding sequence signal by the pulse light modulator, and the signal is divided into two beams by the beam splitter, one of the two beams is used as reference light and detected by the first photoelectric detector, and the other beam is used as probe light and makes the probe light pass through the wavelength division multiplexer and enter the sensing optical fiber, and chaotic Raman backscattering signals generated in the sensing optical fiber and output from the wavelength division multiplexer are detected by the second photoelectric detector, and the sensing method comprises the following steps:

[0037] S1, modulating the continuous chaotic laser into a multi-pulse coding sequence signal, detecting the reference light by the first photoelectric detector, and detecting the chaotic Raman backscattering signals by the second photoelectric detector;

[0038] S2, performing time-domain difference signal reconstruction on the chaotic Raman backscattering signals to obtain chaotic reconstructed Raman backscattering signals in a short scale;

[0039] S3, performing short-scale time-domain correlation compression calculation on the chaotic pulse sequence reference signal and the reconstructed chaotic Raman backscattering signals to obtain a short-scale time-domain correlation compression coefficient;

[0040] S4, keeping the length 2n and the number m of the pulse coding sequence unchanged, changing the pulse coding sequence, repeating steps S1-S3 until all the multi-pulse coding sequences are traversed, and performing accumulation summation operation on all the obtained short-scale time-domain correlation compression coefficients;

[0041] S5, calculating the temperature mutation position L1, the temperature mutation region length ΔL and the temperature information T at the temperature mutation according to the number a0 and a1 of delay sampling points corresponding to the positive peak value and the negative peak value of the short-scale time-domain correlation compression coefficient after summation, and the positive peak value of the short-scale time-domain correlation compression coefficient after summation; the calculation formula is:

[0042]

[0043] ΔL=(a1-a0)·c / (2n0·f s );

[0044]

[0045] wherein c represents the speed of light, n0 represents the refractive index in the optical fiber, f s represents the sampling rate, h is the Planck constant, Δν is the Raman shift, k is the Boltzmann constant, T0 represents the temperature of the sensing optical fiber in the non-temperature change region, This indicates additional loss information at the temperature change location L1. For the attenuation information at sensing fiber L1, C peak The summation of the short-scale time-domain correlation compression coefficients represents the positive peak value, P represents the total power of a single pulse sequence, and K represents the positive peak value. a λ represents the coefficient related to the Raman backscattering anti-Stokes cross section. a λ is the wavelength of the Raman backscattered anti-Stokes signal, and A represents the influence function of the length of the temperature abrupt change region on the positive correlation peak.

[0046] Compared with the prior art, the present invention has the following advantages:

[0047] This invention provides a distributed fiber Raman sensing device and method based on chaotic pulse coding. It involves performing time-domain differential reconstruction of multiple sets of pulse-coded chaotic Raman back-back anti-Stokes scattering signals to obtain chaotic Raman back-back anti-Stokes signals with time-series characteristics consistent with the chaotic detection signal in temperature abrupt change regions along the fiber. Subsequently, the reconstructed chaotic Raman back-back anti-Stokes scattering signals and the chaotic detection signal are subjected to short-scale time-domain correlation compression processing. Finally, the correlation compression signals under multiple pulse sequences are accumulated and summed to locate and demodulate temperature abrupt change points along the fiber based on the correlation peaks. This invention utilizes time-domain differential reconstruction and short-scale time-domain correlation compression methods to eliminate the limitation of pulse width on spatial resolution, enabling the system to achieve millimeter-level spatial resolution. Furthermore, injecting multiple pulses into the fiber increases the fiber input power, strengthens the correlation between the chaotic sequence and the reconstructed signal, multiplies the peak-to-peak value of the chaotic correlation, avoids signal crosstalk, improves the system's signal-to-noise ratio, and enhances temperature accuracy and sensing distance. Attached Figure Description

[0048] Figure 1 This is a schematic diagram of the structure of a distributed fiber Raman sensing device based on chaotic multi-pulse coding provided in Embodiment 1 of the present invention;

[0049] Figure 2 This is a schematic diagram of another structure according to Embodiment 1 of the present invention;

[0050] Figure 3 This is a schematic diagram of the device structure used in a distributed fiber Raman sensing method based on chaotic multi-pulse coding provided in Embodiment 2 of the present invention.

[0051] In the diagram: 1-Semiconductor laser, 2-Circulator, 3-Beam splitter, 4-Polarization controller, 5-Optical attenuator, 6-Optical isolator, 7-Pulse signal generator, 8-Pulse light modulator, 9-Optical amplifier, 10-Beam splitter, 11-First photodetector, 12-Wavelength division multiplexer, 13-Sensing fiber, 14-Second photodetector, 15-Data acquisition card, 16-Computer, 18-Chaotic light source. Detailed Implementation

[0052] 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.

[0053] Example 1

[0054] like Figure 1 As shown, Embodiment 1 of the present invention provides a distributed fiber Raman sensing device based on chaotic multi-pulse coding, comprising: a chaotic light source 18, a pulse light modulator 8, an optical amplifier 9, a beam splitter 10, a first photodetector 11, a wavelength division multiplexer 12, a sensing fiber 13, a second photodetector 14, a data acquisition card 15, and a computer 16. The pulsed light modulator 8 is used to modulate the continuous chaotic laser emitted by the chaotic light source 18 into multiple different multi-pulse sequence optical signals according to the encoded pulse sequence. The multi-pulse sequence optical signals are amplified by the optical amplifier 9 and then split into two beams by the beam splitter 10. One beam serves as a reference beam and is detected by the first photodetector 11. The other beam serves as a probe beam and enters the sensing fiber 13 after passing through ports a and b of the wavelength division multiplexer 12. The chaotic Raman backscattering signal generated in the sensing fiber 13 is detected by the second photodetector 14 after passing through ports b and c of the wavelength division multiplexer 12. The output signals of the first photodetector 11 and the second photodetector 14 are acquired by the data acquisition card 15 and sent to the computer 16. The encoded pulse sequence is a binary code array with a total sequence length of 2n, and each encoded pulse sequence contains m pulses. The encoded sequence is labeled as follows: Total Group-coded pulse sequence.

[0055] The computer 16 is used to calculate the output of the pulse light modulator 8. Under different multi-pulse optical signal conditions, the output signals of the first photodetector 11 and the second photodetector 14 are calculated to locate and demodulate temperature abrupt change points along the optical fiber. Specifically, the computer 16 performs time-domain differential signal reconstruction on the chaotic Raman backscattered signal to obtain a short-scale chaotic Raman backscattered signal. By performing time-domain correlation compression and accumulation operations on multiple sets of chaotic pulse reference signals and the reconstructed chaotic Raman backscattered signal, the computer locates and demodulates temperature abrupt change points along the optical fiber.

[0056] Specifically, in this embodiment, as Figure 2As shown, the chaotic light source includes a semiconductor laser 1, a circulator 2, a beam splitter 3, a polarization controller 4, and an optical attenuator 5. The laser emitted by the semiconductor laser 1 is split into two beams by the beam splitter 3 after passing through the circulator 2. One of the beams serves as feedback light and returns to the semiconductor laser 1 after passing through the polarization controller 4, the optical attenuator 5, and the circulator 2, causing it to output chaotic light. The chaotic light then passes through the circulator 2, the coupler 3, and the optical isolator 6 before being incident on the pulsed light modulator 8. After passing through the pulsed light modulator 8, the continuous chaotic light is converted into a multi-pulse coded sequence signal and amplified by the optical amplifier 9.

[0057] Furthermore, such as Figure 1 As shown, this embodiment of a distributed fiber Raman sensing device based on chaotic multi-pulse coding further includes an optical isolator 6. The optical isolator 6 is disposed at the output port of the chaotic light source and is used to isolate the disturbance of the light source by scattered light in the subsequent optical path. The optical amplifier 9 can specifically be a pulsed erbium-doped fiber amplifier, used to amplify the coded and modulated pulsed light.

[0058] Specifically, in this embodiment, both the beam splitter 10 and the beam splitter 3 can be fiber optic couplers. The beam splitter 10 has a splitting ratio of 1:99, where 1 is the reference light and 99 is the probe light. The beam splitter 3 can have a splitting ratio of 50:50.

[0059] Specifically, in this embodiment, the wavelength of the chaotic light source 18 is 1550nm, the wavelength of port a of the wavelength division multiplexer is 1550nm, the wavelength of port b is 1550nm / 1450nm, and the wavelength of port c is 1450nm. The multi-pulse laser sequence amplified by the optical amplifier 9 is then split into reference light and probe light by the beam splitter. The chaotic pulse laser sequence of the reference path is detected by the first photodetector 11, and the chaotic pulse laser sequence of the probe path enters the sensing fiber 13 after passing through the wavelength division multiplexer 12. Back-scattered chaotic Raman light is generated in the sensing fiber and emitted from the 1450nm port of the wavelength division multiplexer 12, where it is detected by the second photodetector 14. The first photodetector 11 and the second photodetector 14 convert the detected optical signals into electrical signals, which are then acquired by the digital acquisition card 15 and processed by the computer 16.

[0060] Specifically, a distributed fiber Raman sensing device based on chaotic multi-pulse coding in this embodiment further includes a pulse signal generator 7, which is used to emit multiple different coded pulse sequences to drive the pulse light modulator 8.

[0061] The measurement principle of this invention is described below.

[0062] I. Light Intensity Processing of Chaotic Pulse Reference Signal and Chaotic Raman Backscattering Anti-Stokes Signal

[0063] (1) Acquisition and processing of chaotic Raman backscattering signals.

[0064] In temperature demodulation, assuming the laser pulse width is W, the intensity of the backscattered Raman signal (anti-Stokes) at position L of the sensing fiber is:

[0065]

[0066] In the formula, P0 is the incident power of the pulsed laser, that is, the power of a single pulse in a multi-pulse optical signal, and K... a λ represents the coefficient related to the Raman backscattering anti-Stokes backscattering cross section. a The wavelengths of the Raman backscattered anti-Stokes signal, α0, α as These are the loss coefficients per unit length of the incident light and the anti-Stokes light in the sensing fiber, respectively, where L is the position of the sensing fiber, and R... as (T) is the temperature modulation function of the anti-Stokes scattered light:

[0067]

[0068] Where Δν is the Raman frequency shift, h is Planck's constant, k is Boltzmann's constant, and T is the temperature of the sensing fiber.

[0069] In fact, in distributed fiber Raman sensing systems, due to the principles of optical time-domain reflectometry and time-of-flight positioning, the Raman backscattered anti-Stokes signal acquired by the acquisition system at a certain location in the sensing fiber is not the light intensity information modulated by temperature at that point in the sensing fiber, but rather the accumulation of Raman scattered light intensity information excited along the sensing fiber within the pulse width scale. In distributed fiber Raman sensing systems based on broadband chaotic lasers, the broadband chaotic laser has random amplitude characteristics. Therefore, after injecting a chaotic pulse-coded signal with a pulse width of W, a pulse number of 2n, and a coding period of 2nW into the sensing fiber, the intensity of the chaotic Raman backscattered anti-Stokes signal associated with the i-th symbol at position L of the sensing fiber, acquired by the high-speed data acquisition card, can be expressed as:

[0070]

[0071] Among them, P j f is the power of the j-th data point of the chaotic pulse elementary laser. s Where W is the sampling rate. s For chaotic pulse signals at f s Number of unit pulse data points at the sampling rate, W i W represents the pulse width corresponding to i data points. j =j / f s , For location LWj The temperature modulation function value of the anti-Stokes scattered light at c / 2n0 represents the temperature-modulated backscattering factor of anti-Stokes photons per unit length, where c is the speed of light in the sensing fiber and n0 is the refractive index of the sensing fiber. i This represents the value of the i-th symbol in a multi-pulse optical signal. When the symbol is "1", Q represents... i =1, otherwise Q i =0.

[0072] (2) Acquisition and processing of chaotic pulse reference signals.

[0073] The reference signal of the j-th data point associated with the i-th symbol, collected by the acquisition card 15, is:

[0074] I ref (i,j)=Q i ·P j Where 1≤i≤2n, 1≤j≤W·f s (4)

[0075] (3) Reconstruct the chaotic Raman back-stokes scattering signal based on the time-domain differential signal reconstruction method.

[0076] The acquired chaotic Raman back-anti-Stokes scattering signal has each sampling point representing a superposition of the light intensity information of the entire chaotic pulse sequence, and the chaotic signal is constantly changing due to the modulation of the temperature change region of the sensing fiber. Based on this, the back-anti-Stokes scattering signal is reconstructed to obtain the reconstructed chaotic Raman back-anti-Stokes scattering signal. The expression of the time-domain difference reconstruction method is as follows:

[0077]

[0078] Among them, F as (L, j) represents the reconstructed chaotic Raman backscattered anti-Stokes signal at the j-th sampling point at location L.

[0079] Let the temperature of the temperature-changing region be T1, the temperature of the non-temperature-changing region be T0, and the location be L1. Let ΔL be the length (spatial scale) of the temperature-changing region, and its length in the time scale be expressed as Δm. After time-domain difference reconstruction, the reconstructed chaotic Raman backscattering signal in the non-temperature abrupt region is 0, and the reconstructed Raman backscattering signal F at the temperature abrupt point is... as (L1,k) is represented as:

[0080]

[0081] Where k represents the data point corresponding to the temperature abrupt change point. This indicates the additional loss information at the sensing fiber L1. This refers to the attenuation information at the sensing fiber L1. It can be expressed by formula (7):

[0082]

[0083] Where P0 represents the power corresponding to a single pulse. It can be detected using an optical power meter.

[0084] As can be seen from formula (3), each acquired signal point is actually a superposition of optical fibers with a pulse element length. In this embodiment of the invention, the anti-Stokes signal shown in formula (3) is differentially processed by the time-domain differential operation of formula (5). The anti-Stokes signal after time-domain differential is shown in formula (6). Comparing formulas (3) and (6), it can be seen that the anti-Stokes signal after time-domain differential processing is no longer a signal accumulation. This eliminates the spatial resolution problem of pulse width limitation and improves the spatial resolution. Then, correlation is performed to determine the position and temperature of the temperature change zone based on the correlation peak. Therefore, the spatial resolution of the present invention depends on the full width at half maximum (FWHM) of the correlation peak. The FWHM of the chaotic correlation peak depends on the bandwidth of the chaotic signal. The broadband characteristics of the chaotic signal determine that the spatial resolution of the present invention can reach the millimeter level.

[0085] II. Localization is achieved using a short-scale temporal correlation compression method.

[0086] For the chaotic pulse sequence reference signal I ref and reconstructing the chaotic Raman backscattered anti-Stokes signal F as Short-scale time-domain correlation compression is performed to obtain the short-scale time-domain correlation compression coefficient C(a), and then... The short-scale time-domain correlation compression coefficients corresponding to different multi-pulse optical signal sequences are summed, and the position and peak value of the correlation peak are determined based on the summed short-scale time-domain correlation compression coefficients; the specific calculation formula is as follows:

[0087]

[0088] Where M represents the total number of sampling points of the reconstructed chaotic Raman backscattered anti-Stokes signal, and F as (j) represents the reconstructed chaotic Raman backscattered anti-Stokes signal at the j-th sampling point, I ref (i, j+a) represents the chaotic pulse reference signal with a pulse delay corresponding to the i-th symbol in the pulse sequence.

[0089] When the reference signal is delayed by a0 sampling points to the starting point of the temperature abrupt change region, the correlation coefficient shows a positive peak value. Therefore, the location of the temperature abrupt change region can be determined as follows:

[0090]

[0091] When the reference signal is delayed by a1 sampling points to the end of the temperature change region, the correlation coefficient exhibits a negative peak. The length of the temperature change region can be determined based on the difference between the two peak delays. The formula for calculating the length of the temperature change region is as follows:

[0092]

[0093] 3. Short-scale time-domain correlation is used to compress the positive peak demodulation temperature.

[0094] Reference signal I ref The correlation short-scale time-domain compression of the reconstructed chaotic Raman backscattered anti-Stokes scattering signal at the temperature abrupt change location L1 yields the following expression for the positive peak correlation:

[0095] C peak =∑∑I ref F as (L1); (11)

[0096] To analyze the impact of the length of the temperature abrupt change region on the correlation peak, a reference signal autocorrelation function A(Δm) is introduced, which represents the spatial scale length of the temperature abrupt change region in the time scale as Δm. Its expression is:

[0097]

[0098] The influence function A of the length of the temperature abrupt change region on the peak value of the positive correlation can be expressed as:

[0099]

[0100] Right now:

[0101]

[0102] in, This represents a combination of m elements chosen from 2n elements, which characterizes the number of encoded pulse sequences, and is expressed as:

[0103]

[0104] Combining formulas (4) and (6), we expand formula (11), and combine it with formula (13), as well as the formula for the temperature modulation function value. Temperature information in areas of temperature abrupt change can be extracted, and its demodulation equation is shown in formula (16).

[0105]

[0106] Where c represents the speed of light, n0 represents the refractive index of the optical fiber, and f s The sampling rate is represented by h, Planck's constant is h, Δν is the Raman frequency shift is Δν, k is Boltzmann's constant is Δν, and T0 represents the temperature of the sensing fiber in the non-temperature-varying region. This indicates additional loss information at the temperature change location L1. For the attenuation information at sensing fiber L1, C peak The summation of the short-scale time-domain correlation compression coefficients represents the positive peak value, P represents the total power of a single pulse sequence, P = ∑P0; ∑P represents The sum of the total power of the different pulse sequences, K a λ represents the coefficient related to the Raman backscattering anti-Stokes cross section. a λ is the wavelength of the Raman backscattered anti-Stokes signal, and A represents the influence function of the length of the temperature abrupt change region on the positive correlation peak.

[0107] Specifically, in this embodiment, the method for the computer 16 to locate and demodulate the temperature abrupt change point information along the optical fiber is as follows:

[0108] S101. The chaotic Raman backscattering signal is reconstructed by time-domain difference using formula (5) to obtain the chaotic reconstructed Raman backscattering signal at a short scale.

[0109] S102. Using formula (8), the short-scale time-domain correlation compression operation is performed on the chaotic pulse sequence reference signal and the reconstructed chaotic Raman back-stokes scattering signal to obtain the short-scale time-domain correlation compression coefficient.

[0110] S103. Then, sum the short-scale time-domain correlation compression coefficients of all different multi-pulse coded sequence signals to obtain the summed short-scale time-domain correlation compression coefficients.

[0111] S104. Based on the number of delayed sampling points a0 and a1 corresponding to the positive and negative peak values ​​of the summed short-scale time-domain correlation compression coefficients, respectively, and the positive peak value C of the summed short-scale time-domain correlation compression coefficients... peak Calculate the temperature change location L1, the temperature change region length ΔL, and the temperature information T at the temperature change location; the calculation formulas are formulas (9), (10), and (16).

[0112] Specifically, in this embodiment, m = n, that is, the width of the coded pulse sequence is set to 2n, and each coded pulse sequence includes n sequences, the value of n can be 3 to 10. This embodiment of the invention strengthens the correlation between the chaotic sequence and the reconstructed signal through multi-pulse coding, realizes the doubling of the peak-to-peak value of the chaotic correlation, avoids signal crosstalk, improves the signal-to-noise ratio of the system, and enhances the temperature accuracy and sensing distance.

[0113] Example 2

[0114] Embodiment 2 of the present invention provides a distributed fiber Raman sensing method based on chaotic multi-pulse coding, such as... Figure 3 As shown, the apparatus includes a continuous chaotic laser 15, a pulsed light modulator 8, a beam splitter 10, a wavelength division multiplexer 12, a sensing fiber 13, a first photodetector 11, and a second photodetector 14. The continuous chaotic laser output from the continuous chaotic laser 15 is modulated into a multi-pulse coded sequence signal by the pulsed light modulator 8, and then split into two beams by the beam splitter 10. One beam serves as a reference light and is detected by the first photodetector 11. The other beam serves as the detection light and passes through the wavelength division multiplexer 12 into the sensing fiber 13. The second photodetector 14 detects the chaotic Raman backscattered anti-Stokes signal generated in the sensing fiber 13 and output from the wavelength division multiplexer 12. The sensing method includes the following steps:

[0115] S1. The continuous chaotic laser is modulated into a multi-pulse coded sequence signal, and the reference light I is detected by the first photodetector 11. ref The chaotic Raman backscattering signal I is detected by the second photodetector 14. as ;

[0116] S2. The chaotic Raman anti-Stokes scattering signal is reconstructed using the time-domain difference signal through formula (5) to obtain the chaotic reconstructed Raman anti-Stokes scattering signal F at a short scale. as ;

[0117] S3. According to formula (8), the chaotic pulse sequence reference signal I ref and reconstructing the chaotic Raman backscattered anti-Stokes signal F as Short-scale time-domain correlation compression calculations are performed to obtain the short-scale time-domain correlation compression coefficients;

[0118] S4. Keeping the length and number of pulses of the multi-pulse coded sequence unchanged, change the pulse coded sequence and repeat steps S1 to S3 until all multi-pulse coded sequences have been traversed. Summate all the short-scale time-domain correlation compression coefficients obtained. For a multi-pulse coded sequence signal with a length of 2n and a pulse count of m, the number of repetitions is [number missing].

[0119] S5. Based on the number of delayed sampling points a0 and a1 corresponding to the positive and negative peak values ​​of the summed short-scale time-domain correlation compression coefficient, respectively, and the positive peak value of the summed short-scale time-domain correlation compression coefficient, calculate the temperature change location L1, the temperature change region length ΔL, and the temperature information T at the temperature change location; the calculation formulas are formulas (9), (10), and (16).

[0120] Furthermore, the apparatus used in this embodiment may also include a pulse signal generator 7, which is used to generate multiple different coded pulse sequences to drive the pulse light modulator 8. In addition, it may also include an optical isolator disposed at the output port of the chaotic light source, and an optical amplifier disposed at the output port of the pulse light modulator 8.

[0121] In summary, this application provides a distributed fiber Raman sensing device and method based on chaotic multi-pulse coding. It modulates pulsed light using multiple sets of different coded pulse sequences, performs time-domain differential reconstruction of the chaotic Raman backscattered signals from these sequences, and obtains chaotic Raman anti-Stokes signals consistent with the temporal characteristics of the chaotic detection signal in temperature abrupt change regions along the fiber. Subsequently, the reconstructed chaotic Raman backscattered signal and the chaotic detection signal undergo short-scale time-domain correlation compression processing. Finally, the correlated compressed signals from multiple pulse sequences are summed, and the temperature abrupt change points along the fiber are located and demodulated based on the correlation peaks. The time-domain differential reconstruction method and the short-scale time-domain correlation compression method eliminate the limitation of pulse width on spatial resolution, enabling the system to achieve millimeter-level spatial resolution. Pulse coding increases the input power to the fiber, strengthens the correlation between the chaotic sequence and the reconstructed signal, multiplies the peak-to-peak value of the chaotic correlation, avoids signal crosstalk, improves the system's signal-to-noise ratio, and enhances temperature accuracy and sensing distance.

[0122] 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 distributed fiber Raman sensing device based on chaotic multi-pulse coding, characterized in that, include: Chaotic light source (18), pulse light modulator (8), optical amplifier (9), beam splitter (10), first photodetector (11), wavelength division multiplexer (12), sensing fiber (13), second photodetector (14), data acquisition card (15), computer (16). The pulsed light modulator (8) is used to modulate the continuous chaotic laser emitted by the chaotic light source (18) into multiple different multi-pulse sequence optical signals according to the encoded pulse sequence. The multi-pulse sequence optical signals are amplified by the optical amplifier (9) and then split into two beams by the beam splitter (10). One beam is used as a reference light and is detected by the first photodetector (11). The other beam is used as a probe light and enters the sensing fiber (13) after passing through the a and b ports of the wavelength division multiplexer (12). The chaotic Raman backscattering signal generated in the sensing fiber (13) is detected by the second photodetector (14) after passing through the b and c ports of the wavelength division multiplexer (12). The output signals of the first photodetector (11) and the second photodetector (14) are collected by the data acquisition card (15) and sent to the computer (16). The encoded pulse sequence is a binary code array with a total sequence length of 2n and the number of pulses contained in each encoded pulse sequence is m. The computer (16) is used to output the pulse light modulator (8). Under different multi-pulse sequence optical signal conditions, the output signals of the first photodetector (11) and the second photodetector (14) are calculated to locate and demodulate the temperature change point information along the optical fiber. The specific method for the computer (16) to locate and demodulate the temperature abrupt change point information along the optical fiber is as follows: S101. Perform time-domain difference signal reconstruction on the chaotic Raman backscattering anti-Stokes signal to obtain the chaotic reconstructed Raman backscattering anti-Stokes signal at a short scale. S102. Perform short-scale time-domain correlation compression operation on the chaotic pulse sequence reference signal and the reconstructed chaotic Raman back-stokes scattering signal to obtain the short-scale time-domain correlation compression coefficient. S103. Then, sum the short-scale time-domain correlation compression coefficients of all different multi-pulse coded sequence signals to obtain the summed short-scale time-domain correlation compression coefficients. S104. The number of delayed sampling points corresponding to the positive and negative peak values ​​of the summed short-scale time-domain correlation compression coefficients. a 0 and a 1. Calculate the positive peak value of the short-scale time-domain correlation compression coefficient after summation, and calculate the temperature abrupt change location L1, the length ΔL of the temperature abrupt change region, and the temperature information at the temperature change point. T ; The calculation formula is: ； ； ； in, c n represents the speed of light, n0 represents the refractive index in the optical fiber, and f represents the speed of light. s Indicates the sampling rate. h Let be Planck's constant. Δν For Raman frequency shift, k Boltzmann's constant, T 0 Indicates the temperature of the sensing fiber in the non-temperature-varying region. Δ φ( L 1) Indicates the location of temperature change L 1 additional loss information, φ( L 1) For sensing optical fiber L 1 Attenuation information at that location, C peak The summation represents the positive peak value of the short-scale time-domain correlation compression coefficient, and P represents the total power of a single pulse sequence. K a This represents the coefficients related to the Raman backscattering anti-Stokes cross section. λ a It is the wavelength of the Raman backscattered anti-Stokes signal. A This function represents the influence of the length of the temperature abrupt change region on the peak value of the positive correlation.

2. The distributed fiber Raman sensing device based on chaotic multi-pulse coding according to claim 1, characterized in that, The chaotic light source (18) includes a semiconductor laser (1), a circulator (2), a beam splitter (3), a polarization controller (4), and an optical attenuator (5). The laser emitted by the semiconductor laser (1) is split into two beams by the beam splitter (3) after passing through the circulator (2). One beam is used as feedback light and passes through the polarization controller (4), the optical attenuator (5), and the circulator (2) before returning to the semiconductor laser (1) to output chaotic light. The other beam is used as the output of the chaotic light source.

3. The distributed fiber Raman sensing device based on chaotic multi-pulse coding according to claim 1, characterized in that, It also includes an optical isolator (6), which is located at the output port of the chaotic light source.

4. The distributed fiber Raman sensing device based on chaotic multi-pulse coding according to claim 1, characterized in that, The wavelength of the chaotic light source is 1550nm, the wavelength of port a of the wavelength division multiplexer is 1550nm, the wavelength of port b is 1550nm / 1450nm, and the wavelength of port c is 1450nm.

5. The distributed fiber Raman sensing device based on chaotic multi-pulse coding according to claim 1, characterized in that, It also includes a pulse signal generator (7) for emitting multiple different coded pulse sequences to drive the pulse light modulator (8).

6. The distributed fiber Raman sensing device based on chaotic multi-pulse coding according to claim 1, characterized in that, The formula for calculating the influence function A of the length of the temperature abrupt change region on the positive correlation peak is: in, P j W represents the power of the j-th data point, and W represents the pulse width. This represents the value of the i-th symbol in the coded pulse sequence; Δm The length of the temperature abrupt change region over a time scale; Temperature change location L The formulas for calculating attenuation information and additional loss information are as follows: ； ； in, Let P0 represent the temperature modulation function of the Raman backscattered anti-Stokes light, and P0 represent the power of a single pulse. α 0 , α as These represent the loss coefficients per unit length of the incident light and the anti-Stokes light in the sensing fiber, respectively.

7. The distributed fiber Raman sensing device based on chaotic multi-pulse coding according to claim 1, characterized in that, In step S101, the calculation formula for time-domain differential signal reconstruction is as follows: N-1； in, F as ( L , j () represents the reconstructed chaotic Raman backscattered anti-Stokes signal at the j-th sampling point at location L; and Indicates position The chaotic Raman backscattered anti-Stokes signal at position L; N represents the number of fiber sampling points; In step S102, the formula for calculating the short-scale time-domain correlation compression coefficient is as follows: ； Among them, C ( a () represents the short-scale time-domain correlation compression coefficient. M This represents the total number of sampling points in the reconstructed chaotic Raman backscattered anti-Stokes signal. F as ( j () represents the reconstructed chaotic Raman backscattered anti-Stokes signal at the j-th sampling point. This represents the chaotic pulse reference signal corresponding to the i-th symbol in the pulse sequence with a pulse delay of a sampling points.

8. The distributed fiber Raman sensing device based on chaotic multi-pulse coding according to claim 1, characterized in that, m=n, meaning the length 2n of the encoded pulse sequence is twice the number of pulses m.

9. A distributed fiber Raman sensing method based on chaotic multi-pulse coding, characterized in that, The apparatus used includes a chaotic light source (18), a pulsed light modulator (8), a beam splitter (10), a wavelength division multiplexer (12), a sensing fiber (13), a first photodetector (11), and a second photodetector (14). The continuous chaotic laser output from the continuous chaotic laser (15) is modulated into a multi-pulse coded sequence signal by the pulsed light modulator (8), and then split into two beams by the beam splitter (10). One beam is used as a reference light and is detected by the first photodetector (11). The other beam is used as a detection light and is passed through the wavelength division multiplexer (12) into the sensing fiber (13). The second photodetector (14) detects the chaotic Raman backscattered anti-Stokes signal generated in the sensing fiber (13) and output from the wavelength division multiplexer (12). The sensing method includes the following steps: S1. The continuous chaotic laser is modulated into a multi-pulse coded sequence signal, and the reference light is detected by the first photodetector (11), and the back-to-Stokes scattering signal after the chaotic Raman is detected by the second photodetector (14). S2. Perform time-domain difference signal reconstruction on the chaotic Raman backscattering anti-Stokes signal to obtain the chaotic reconstructed Raman backscattering anti-Stokes signal at a short scale. S3. Perform short-scale time-domain correlation compression calculation on the chaotic pulse sequence reference signal and the reconstructed chaotic Raman back-stokes scattering signal to obtain the short-scale time-domain correlation compression coefficient. S4. Keep the length 2n and the number of pulses m of the multi-pulse coding sequence unchanged, change the pulse coding sequence, and repeat steps S1 to S3 until all multi-pulse coding sequences are traversed. Then, sum all the short-scale time-domain correlation compression coefficients obtained. S5. Based on the number of delayed sampling points a0 and a1 corresponding to the positive and negative peak values ​​of the summed short-scale time-domain correlation compression coefficient, respectively, and the positive peak value of the summed short-scale time-domain correlation compression coefficient, calculate the temperature abrupt change location L1, the length ΔL of the temperature abrupt change region, and the temperature information at the temperature change point. T The calculation formula is: ； ； ； Where c represents the speed of light, n0 represents the refractive index of the optical fiber, and fs represents the sampling rate. h Let be Planck's constant. Δν For Raman frequency shift, k Boltzmann's constant, T0 Indicates the temperature of the sensing fiber in the non-temperature-varying region, Δφ( L 1) Indicates the location of temperature change L 1 additional loss information, φ( L 1) For sensing optical fiber L1 Attenuation information at that location, Cpeak The summation represents the positive peak value of the short-scale time-domain correlation compression coefficient, and P represents the total power of a single pulse sequence. Ka This represents the coefficients related to the Raman backscattering anti-Stokes cross section. λa It is the wavelength of the Raman backscattered anti-Stokes signal. A This function represents the influence of the length of the temperature abrupt change region on the peak value of the positive correlation.

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