Raman distributed optical fiber temperature measurement system and method based on strong autocorrelation pulse coding

Abstract

The invention relates to the technical field of distributed optical fiber sensing, and discloses a Raman distributed optical fiber temperature measurement system based on strong autocorrelation pulse coding, which comprises a continuous laser device, a high autocorrelation pulse coding module, a high autocorrelation pulse coding module, a high autocorrelation pulse coding module and a high autocorrelation pulse coding module, the pulsed light is amplified by an erbium-doped optical fiber amplifier and then enters a sensing optical fiber through a wavelength division multiplexer, Raman backward scattering light generated in the sensing optical fiber is output by the wavelength division multiplexer and then is detected by a photoelectric detector, and a detection signal is collected by a data collection card and then is sent to a computer; the signal generator is used for driving the optical amplifier to carry out strong autocorrelation pulse code modulation on continuous laser output by the continuous laser, and the computer is used for calculating temperature information along the sensing optical fiber according to received single-pulse backward Raman scattering light signals corresponding to four groups of coding sequences. According to the invention, small spatial resolution can be realized in a long-distance distributed sensing system.

Description

Technical Field

[0001] The present invention relates to the technical field of distributed optical fiber sensing, and particularly to a Raman distributed optical fiber temperature measurement system and method based on strongly self-correlated pulse coding, which uses strongly self-correlated pulse coding to optimize a long-distance distributed optical fiber sensing system, can achieve better spatial resolution at long distances, and solves the problem of mutual restriction between the existing sensing distance and spatial resolution. Background Art

[0002] A distributed optical fiber Raman sensing system can continuously measure the distributed temperature characteristic information along a sensing optical fiber. Its main principle is to use the ambient temperature along the sensing optical fiber to intensity-modulate the Raman scattered light in the optical fiber. The system can obtain the distributed temperature information along the sensing optical fiber by collecting this Raman scattered light carrying temperature information. The distributed optical fiber Raman sensing system has the advantages of strong environmental adaptability, anti-electromagnetic interference, large detection range, high temperature accuracy, etc., and is therefore widely used in temperature safety monitoring fields such as electric power, transportation, fire protection, petrochemical industry, and aerospace.

[0003] Currently, distributed optical fiber sensing systems mainly use three scattering effects in optical fibers, namely Rayleigh, Brillouin, and Raman, to achieve distributed sensing. Among them, spontaneous Raman scattering is a signal with extremely weak intensity (its optical intensity is only -50 dB of the incident signal), so the signal power collected by the receiving end is very low. Based on this, distributed optical fiber sensing systems generally require very high pump light pulse power to improve the signal-to-noise ratio (SNR) of the received signal. However, further increasing the pulse emission power is restricted by fiber nonlinear effects such as self-phase modulation, which causes a large attenuation of the pulse power and serious distortion of the waveform, resulting in measurement errors. In addition, if an erbium-doped fiber amplifier is used to amplify the pulse signal twice, due to the generation of the transient effect of the erbium-doped fiber amplifier, the pulse optical signal will be distorted before it enters the sensing optical fiber. Therefore, there is a technical bottleneck in the distributed optical fiber sensing system where the peak power of the pulse and the signal-to-noise ratio of the sensing signal restrict each other, that is, there is an input threshold for the peak power of the pulsed light.

[0004] In summary, it is necessary to improve the existing Raman distributed optical fiber temperature measurement system to solve the technical bottleneck that the existing sensing system cannot balance the sensing distance and spatial resolution. Summary of the Invention

[0005] In order to solve the technical bottlenecks existing in the existing distributed optical fiber Raman sensing system, such as the inability to break through the emission threshold of pulsed light and the inability to balance the sensing distance and spatial resolution, the present invention proposes a Raman distributed temperature measurement system and method based on strong self-correlation coding, which realizes Raman temperature measurement through strong self-correlation coding to break through the threshold limit of the peak power of pulsed light and eliminate the influence of the transient effect of the erbium-doped fiber amplifier on the waveform of the pulsed light signal.

[0006] In order to solve the above technical problems, the technical solution adopted by the present invention is as follows: a Raman distributed optical fiber temperature measurement system based on strong self-correlation pulse coding, comprising: a continuous laser, an optical amplifier, a signal generator, an erbium-doped fiber amplifier, a wavelength division multiplexer, a photodetector, a data acquisition card, a computer, and a sensing optical fiber. The continuous laser output by the continuous laser becomes pulsed light after passing through the amplifier. The pulsed light is amplified by the erbium-doped fiber amplifier and then enters the sensing optical fiber through the wavelength division multiplexer. The Raman backscattered light generated in the sensing optical fiber is output through the wavelength division multiplexer and is detected by the photodetector. The detected signal is collected by the data acquisition card and then sent to the computer.

[0007] The signal generator is used to drive the optical amplifier to perform strong self-correlation pulse coding modulation on the continuous laser output by the continuous laser. The coding sequences adopted by the strong self-correlation pulse coding modulation are four groups, which are respectively:

[0008]

[0009] Among them, U 1 , W 1 , U 2 , W 2 are respectively one of the coding sequences, A k and B k are two codewords of length k; A k *A k +B k *B k =2Mδ, where "*" represents the correlation operation, M represents the codeword length, and δ is the impulse function;

[0010] The computer is used to calculate the temperature information along the sensing optical fiber according to the single-pulse backward Raman scattered light signals corresponding to the four groups of coding sequences received.

[0011] The calculation formula for the computer to calculate the temperature information along the sensing optical fiber is:

[0012]

[0013] Among them, T represents the temperature to be measured, T 0 represents the temperature in the calibration stage, RBS(T 0) and RBS(T) represent the equivalent single - pulse Raman back - scattered optical signal intensities in the calibration stage and the measurement stage, respectively.

[0014] The calculation formula for the equivalent single - pulse Raman back - scattered optical signal intensity is:

[0015]

[0016] Among them, u, w, and are the single - pulse Raman back - scattered optical signals corresponding to the coding sequences U 1 , W 1 , U 2 , W 2 respectively.

[0017] The coding sequences U 1 , W 1 , U 2 , W 2 The corresponding single - pulse back - Raman back - scattered optical signals u, w, and The calculation formula is:

[0018]

[0019]

[0020] Among them, RBS'(U 1 ), RBS'(U 2 ), RBS'(W 1 ), RBS'(W 1 ) represent the single - pulse Raman back - scattered optical signals corresponding to the coding sequences U 1 , W 1 , U 2 , W 2 received by the photodetector respectively. fft represents the Fourier transform, ifft represents the inverse Fourier transform, and F' represents the result of the Fourier transform of the attenuation envelope f.

[0021] The calculation formula for the computer to calculate the measurement position is:

[0022]

[0023] L represents the measurement position, c represents the speed of light in vacuum, n represents the refractive index of the medium, and t represents the time from signal emission to return.

[0024] The wavelength - division multiplexer is used to output the Raman back - anti - Stokes scattered optical signal generated in the sensing optical fiber and send it to the photodetector.

[0025] The wavelength of the continuous laser is 1550 nm, the photodetector is an avalanche photodetector with a bandwidth of 200 MHz; the sampling rate of the acquisition card is 1 GSa / s; the sensing optical fiber is a single-mode optical fiber.

[0026] In addition, the present invention also provides a Raman distributed optical fiber temperature measurement method based on strongly self-correlated pulse coding, which is implemented based on the Raman distributed optical fiber temperature measurement system based on strongly self-correlated pulse coding, and includes the following steps:

[0027] Step 1: In the calibration stage, set the temperature in the sensing optical fiber to T 0 , drive the optical amplifier by a signal generator to perform strongly self-correlated pulse coding modulation on the continuous laser output by the continuous laser; receive the single-pulse Raman backscattering optical signal corresponding to each coding sequence through the photodetector;

[0028] Step 2: In the measurement stage, drive the optical amplifier by a signal generator to perform strongly self-correlated pulse coding modulation on the continuous laser output by the continuous laser; receive the single-pulse Raman backscattering optical signal corresponding to each coding sequence through the photodetector;

[0029] Step 3: Calculate the intensity of the equivalent single-pulse Raman backscattering optical signal according to the single-pulse Raman backscattering optical signals corresponding to each coding sequence obtained in the calibration stage and the measurement stage; the calculation formula for the intensity of the equivalent single-pulse Raman backscattering optical signal is:

[0030]

[0031] where, u, w and are respectively the single-pulse backscattering Raman anti-Stokes optical signals corresponding to the coding sequences U 1 , W 1 , U 2 , W 2 ;

[0032] Step 4: Calculate the temperature information along the sensing optical fiber according to the intensity of the equivalent single-pulse Raman backscattering optical signal, and the calculation formula is:

[0033]

[0034] where, T represents the temperature to be measured, T 0 represents the temperature in the calibration stage, and RBS(T 0 ) and RBS(T) respectively represent the intensities of the equivalent single-pulse Raman backscattering optical signals in the calibration stage and the measurement stage.

[0035] The coding sequences U 1 , W 1 , U2 , W 2 The corresponding single pulse Raman backscattered light signal u, w and The calculation formula is:

[0036]

[0037] Among them, RBS'(U 1 )、RBS'(U 2 )、RBS'(W 1 )、RBS'(W 1 ) represent the coding sequence U received by the photodetector 1 , W 1 , U 2 , W 2 The corresponding single-pulse Raman backscattered light signal, fft represents Fourier transform, ifft represents inverse Fourier transform, and F' represents the result of Fourier transform of the attenuation envelope f.

[0038] Compared with the prior art, the present invention has the following beneficial effects:

[0039] The present invention proposes a Raman distributed temperature sensing system and method based on strong autocorrelation pulse coding, which breaks through the threshold limit of the peak power of the pulse light by performing strong autocorrelation modulation on the pulse light signal, thereby achieving a higher spatial resolution; in addition, the present invention also performs Fourier operation and inverse Fourier operation on the collected Raman backscattered signal according to the attenuation envelope, eliminating the influence of the transient effect of the erbium-doped fiber amplifier on the pulse light signal waveform, thereby solving the technical bottleneck of the existing sensing system that the sensing distance and spatial resolution cannot be taken into account at the same time. The present invention can achieve a smaller spatial resolution in a long-distance distributed sensing system. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 A schematic structural diagram of a Raman distributed optical fiber temperature measurement system based on strong autocorrelation pulse coding provided by an embodiment of the present invention;

[0041] Figure 2 A schematic flow chart of a Raman distributed optical fiber temperature measurement method based on strong autocorrelation pulse coding provided by an embodiment of the present invention;

[0042] In the figure: 1: continuous laser, 2: optical amplifier, 3: signal generator, 4: erbium-doped fiber amplifier, 5: wavelength division multiplexer, 6: photodetector, 7: data acquisition card, 8: computer, 9: sensor fiber. DETAILED DESCRIPTION

[0043] 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. Apparently, the described embodiments are only a part rather than all of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0044] Embodiment 1

[0045] As Figure 1 shown, Embodiment 1 of the present invention provides a Raman distributed optical fiber temperature measurement system based on strongly self - correlated pulse coding, including: a continuous laser 1, an optical amplifier 2, a signal generator 3, an erbium - doped fiber amplifier 4, a wavelength division multiplexer 5, a photodetector 6, a data acquisition card 7, a computer 8, and a sensing optical fiber 9. The continuous laser output by the continuous laser 1 becomes pulsed light after passing through the optical amplifier 2. The pulsed light is amplified by the erbium - doped fiber amplifier 4 and then enters the sensing optical fiber 9 through the wavelength division multiplexer 5. The Raman back - scattered light generated in the sensing optical fiber 9 is output through the wavelength division multiplexer 5 and detected by the photodetector 6. The detected signal is collected by the data acquisition card 7 and then sent to the computer 8.

[0046] The signal generator 3 is used to drive the optical amplifier 2 to perform strongly self - correlated pulse coding modulation on the continuous laser output by the continuous laser 1. The coding sequences used for the strongly self - correlated pulse coding modulation have four groups, which are U 1 , W 1 , U 2 , W 2 . The computer 8 is used to calculate the temperature information along the sensing optical fiber according to the single - pulse back - scattered Raman light signals corresponding to the four groups of coding sequences received.

[0047] Specifically, in this embodiment, the four groups of coding sequences are respectively:

[0048]

[0049] Among them, U 1 , W 1 , U 2 , W 2 are respectively one of the coding sequences, A k and B k are two codewords with length k; A k *A k +B k *B k =2Mδ, where "*" represents the correlation operation, M represents the codeword length, and δ is the impulse function.

[0050] Specifically, in this embodiment, the wavelength division multiplexer 5 is used to output the Raman back anti-Stokes scattered optical signal generated in the sensing optical fiber 9 and send it to the photodetector 6.

[0051] Specifically, the continuous laser 1 is a semiconductor laser with an output wavelength of 1550 nm, the photodetector 6 is an avalanche photodetector with a bandwidth of 200 MHz; the acquisition card 7 has 2 channels and a sampling rate of 1 GSa / s; the sensing optical fiber 9 is a single-mode optical fiber with a length of 70 km. The first port of the wavelength division multiplexer 5 is connected to the erbium-doped fiber amplifier 4 with a wavelength of 1550 nm, the second port is connected to the photodetector 6 with a wavelength of 1450 nm, and the third port is connected to the sensing optical fiber with a wavelength of 1450 nm / 1550 nm. The optical amplifier 2 is a semiconductor optical amplifier.

[0052] The measurement principle of the embodiment of the present invention is introduced below.

[0053] 1. Acquisition and processing of traditional Raman back anti-Stokes signals:

[0054] In a traditional Raman distributed temperature measurement system, the temperature is monitored by collecting the Raman backscattered signals along the optical fiber. When the pulsed light is incident on the sensing optical fiber, the incident photons collide inelastically with the optical fiber medium to generate Raman Stokes light and Raman anti-Stokes light. Compared with Stokes light, anti-Stokes light is more sensitive to temperature signals. Therefore, the temperature is demodulated and processed by collecting anti-Stokes light. At room temperature, the power of the anti-Stokes light excited by the pulsed light in the optical fiber is:

[0055]

[0056] At any temperature T, the power of the anti-Stokes light at this time is:

[0057]

[0058] In the formula, P 0 is the incident optical power, Γ AS is the scattering coefficient of the back Stokes light, v AS is the frequency of the anti-Stokes photons, h is Planck's constant, Δv represents the Raman frequency shift, and k is the Boltzmann constant. T and T 0 are the temperature to be measured and the normal temperature respectively, a 0 , a AS are the loss coefficients of the incident light and the back anti-Stokes light in the optical fiber, and L is the measurement distance at a certain point on the optical fiber.

[0059] Comparing the two obtained power curves, we can get:

[0060]

[0061] Thus, the temperature distribution curve can be obtained:

[0062]

[0063] Meanwhile, according to the optical time domain reflectometry principle, assuming the speed of light in a vacuum environment is v and the refractive index of the medium is n, and based on the time t taken for the transmitted signal to return, the position of the area to be measured is:

[0064]

[0065] 2. Processing of Raman backscattered Stokes signals based on strongly autocorrelated pulse coding:

[0066] In an embodiment of the present invention, a Raman distributed optical fiber sensing system based on strongly autocorrelated pulse coding, its main principle is to encode pulse signals. Since the signal-to-noise ratio of the received signal is proportional to the total energy of the signal, therefore, when the power is limited, the signal-to-noise ratio can be improved by increasing the time length of the signal. For this purpose, it is necessary to increase the pulse width of the pump optical pulse signal in distributed optical fiber sensing, but this will lead to a reduction in spatial resolution. Therefore, relying solely on a single pulse, the measurement accuracy and spatial resolution of the system will restrict each other. Therefore, a method based on a strongly autocorrelated pulse coding sequence is proposed. The coded pulse sequence has a very high total energy, which can effectively improve the signal-to-noise ratio of the received signal. At the same time, the spatial resolution of the system is only determined by the width of a single symbol pulse in the pulse sequence, which can ensure a relatively high spatial resolution.

[0067] The continuous laser 1 is modulated by the signal generator 3 to modulate the continuous laser into a pulsed light of a strongly autocorrelated pulse coding sequence. Each group of codewords in the strongly autocorrelated sequence is 1 and -1 respectively, and the lengths are equal. The sum of the autocorrelation functions is δ, satisfying:

[0068] A k *A k +B k *B k = 2Mδ; (7)

[0069] Wherein, A k and B k are a group of two codewords of length k, "*" represents the correlation operation, M represents the codeword length, and δ is the impulse function.

[0070] Since only unipolar pulses can be transmitted in the optical fiber, that is, the optical signal intensity cannot be negative, it is necessary to add an offset to the unipolar pulse sequence to convert it into a bipolar complementary sequence U 1 、U 2 、W 1 and W 2 :

[0071]

[0072] The initial sequence is obtained by subtracting four groups of sequences respectively:

[0073]

[0074] The unipolar pulsed light encoded according to the four sequences in formula (7) by the signal generator 3 is respectively injected into the optical fiber. The incident photons collide inelastically with the optical fiber medium to generate backward anti-Stokes light. Under the condition of not considering attenuation, the photodetector obtains four segments of backward scattering signals u, w, and Perform correlation operations on them:

[0075]

[0076] where RBS a , RBS n are the single-pulse backward scattering signals corresponding to codewords A k and B k , is the convolution operation, and h k is the input pulse response.

[0077] Adding the two correlation results in formula (10) can obtain the equivalent single-pulse backward scattering signal:

[0078]

[0079] Therefore, the temperature demodulation formula obtained by using strongly self-correlated pulse coding is:

[0080]

[0081] where T represents the temperature to be measured, and T 0 represents the temperature in the calibration stage. RBS(T 0 ) and RBS(T) respectively represent the equivalent single-pulse Raman backward scattering optical signal intensities in the calibration stage and the measurement stage. The calculation formula for the equivalent single-pulse Raman backward scattering optical signal intensity is:

[0082]

[0083] where u, w, and are respectively the single-pulse backward Raman anti-Stokes optical signals corresponding to the coding sequences U 1 , W 1 , U 2 , W 2 .

[0084] Therefore, it can be seen from formula (11) that, compared with the traditional Raman distributed temperature measurement system, the final response of the Raman distributed temperature measurement system based on strong self-correlation pulse coding provided by the embodiments of the present invention is 2M times that of the single-pulse response, and the spatial resolution is the same as that of the single-pulse response. Therefore, the threshold emission power of the pulsed light can be broken through, so as to achieve a higher spatial resolution.

[0085] 3. Temperature demodulation based on transient effect elimination:

[0086] When performing Raman distributed temperature measurement based on strong self-correlation pulse coding, since the maximum optical power allowed to pass through the optical amplifier 2 is 1 mW, and in order to achieve a higher optical power and a longer sensing distance, an erbium-doped fiber amplifier 4 is generally added to the optical path after the optical amplifier 2. However, experiments have found that transient effects will occur during the operation of the erbium-doped fiber amplifier, which will cause distortion of the coded pulses, manifested as attenuation of the amplified coded pulses, and the longer the timing of the coded pulses, the more serious the attenuation phenomenon.

[0087] By analyzing the attenuation envelope, it can be found that there is a functional relationship f between the attenuation signal and the original signal, satisfying:

[0088]

[0089] Among them, U 1 , W 1 , U 2 , W 2 are four sections of coded pulses formed after being coded by the signal generator 3 and the optical amplifier 2. U 1 (f), U 2 (f), W 1 (f) and W 2 (f) are respectively four sections of coded pulses affected by the transient effect of the erbium-doped fiber amplifier 4, f is the attenuation envelope of the transient effect, and the four sections of backscattering signals excited by the four sections of coded pulses affected and entering the sensing fiber are:

[0090]

[0091] Among them, RBS'(U 1 ), RBS'(U 2 ), RBS'(W 1 ), RBS'(W 2 ) are the backscattering signals excited by the four sections of coded pulses in the sensing fiber, which can be obtained from the received signals of the photodetector 6, and h k is the pulse response.

[0092] It can be seen that the coded pulses affected by the transient effect will destroy the autocorrelation characteristics of the complementary sequence (i.e., Equation (7) does not hold), affect the intensity and dynamic range of the backscattered signal, affect the effective sensing distance, and deteriorate the temperature measurement accuracy of the system. Therefore, in this embodiment, a method for eliminating the influence of the transient effect on the backscattered signal is further proposed, which restores the autocorrelation characteristics of the coded sequence through an algorithm. The specific process is as follows.

[0093] Taking one of the coded sequences U 1 as an example, construct a function:

[0094]

[0095] Convert the product operation of the attenuation envelope f of the erbium-doped fiber amplifier transient effect into the convolution operation of the function f', for subsequent demodulation processing. At this time, the functional relationship of f' is:

[0096]

[0097] where, "fft" is the Fourier transform, "ifft" is the inverse Fourier transform, and U is the coded sequence U 1 The result after Fourier transform. The backscattered signal after Fourier transform is:

[0098]

[0099] Then, convert the convolution operation into a product operation through Fourier transform, and the backscattered signal is transformed into:

[0100] fft[RBS'(U 1 )] = F'·U·H k ; (19)

[0101] where, F', U, and H k are the results of f, U 1 and h k after Fourier transform, respectively. The processed backscattered signal can be restored to the Fourier transform of the backscattered signal excited by the coded sequence U 1 not affected by the transient effect, that is:

[0102]

[0103] Then, perform the inverse Fourier transform on Equation (20), and the restored backscattered signal can be obtained:

[0104]

[0105] For the other three groups of coded sequences W 1 , U 2 , W2 The corresponding backscattering signals RBS'(U 2 ), RBS'(W 1 ), RBS'(W 1 ) can obtain four backscattering signals not affected by the transient effect after performing the same function operation, that is:

[0106]

[0107] Among them, RBS'(U 1 ), RBS'(U 2 ), RBS'(W 1 ), RBS'(W 1 ) respectively represent the single-pulse Raman backscattering optical signals corresponding to the coding sequences U 1 , W 1 , U 2 , W 2 received by the photodetector (6). fft represents the Fourier transform, ifft represents the inverse Fourier transform, and F' represents the result after the Fourier transform of the attenuation envelope f.

[0108] Then, the u, w, and calculated from formulas (21) to (24) are used as the single-pulse backward Raman anti-Stokes optical signals corresponding to the coding sequences U 1 , W 1 , U 2 , W 2 . After performing correlation operations and adding them, that is, substituting into formula (13), the equivalent single-pulse backscattering signal can be obtained. At this time, combined with formula (12) for demodulation processing, the temperature distribution curve can be obtained. By processing with strongly self-correlated pulse coding, the influence of the transient effect of the erbium-doped fiber amplifier can be eliminated, the inherent error of the device can be improved, and thus the effective sensing distance and temperature measurement accuracy of the system can be significantly improved, and the performance index of the system can be greatly improved.

[0109] In addition, without considering the attenuation envelope of the erbium-doped fiber amplifier 4, the single-pulse Raman backscattering optical signals RBS'(U 1 ), RBS'(U 2 ), RBS'(W 1 ), RBS'(W 1 ) detected by the photodetector 6 can also be directly used as the single-pulse Raman backward optical signals corresponding to each coding sequence U 1 , W 1 , U 2 , W 2 . Substitute into formula (13) to calculate the equivalent single-pulse backscattering signal.

[0110] Example 2

[0111] like Figure 2 As shown, the second embodiment of the present invention provides a Raman distributed optical fiber temperature measurement method based on strong autocorrelation pulse coding, which is implemented based on the Raman distributed optical fiber temperature measurement system based on strong autocorrelation pulse coding described in the first embodiment, and includes the following steps:

[0112] Step 1: Calibration stage: Set the temperature in the sensing fiber to T 0 , driving the optical amplifier 2 through the signal generator 3 to perform strong autocorrelation pulse code modulation on the continuous laser output by the continuous laser 1; receiving the single pulse Raman backscattered light signal corresponding to each coding sequence through the photodetector;

[0113] Step 2: In the measurement phase, the signal generator 3 is used to drive the optical amplifier 2 to perform strong autocorrelation pulse code modulation on the continuous laser output by the continuous laser 1; the single pulse Raman backscattered light signal corresponding to each coding sequence is received by the photodetector;

[0114] Step 3: Calculate the temperature information along the sensing optical fiber according to the single pulse Raman backscattered light signals corresponding to each coding sequence obtained in the calibration stage and the measurement stage. The calculation formula is the above formula (12) and (13).

[0115] Wherein, without considering the influence of the transient effect of the erbium-doped fiber amplifier 4 on the waveform of the pulse light signal, the single pulse Raman backscattered light signal RBS′ (U 1 )、RBS'(U 2 )、RBS'(W 1 )、RBS'(W 1 ) as each coding sequence U 1 , W 1 , U 2 , W 2 The corresponding single-pulse Raman backscattered light signal is substituted into formula (13) to calculate the equivalent single-pulse backscattered signal.

[0116] In addition, considering the influence of the transient effect of the erbium-doped fiber amplifier 4 on the pulse light signal waveform, the coding sequence U 1 , W 1 , U 2 , W 2 The corresponding single pulse Raman backscattered light signal u, w and The calculation formula is as above formula (21)~(24).

[0117] In summary, the present invention proposes a Raman distributed temperature sensing system and method based on strong autocorrelation pulse coding, which breaks through the threshold limit of the peak power of the pulse light by performing strong autocorrelation modulation on the pulse light signal, thereby achieving a higher spatial resolution. In addition, the present invention also performs Fourier operation and inverse Fourier operation on the collected Raman backscattered signal according to the attenuation envelope, eliminating the influence of the transient effect of the erbium-doped fiber amplifier on the waveform of the pulse light signal, thereby solving the technical bottleneck of the existing sensing system that the sensing distance and spatial resolution cannot be taken into account at the same time. The present invention can achieve a smaller spatial resolution in a long-distance distributed sensing system.

[0118] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements 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 Raman distributed optical fiber temperature measurement system based on strong autocorrelation pulse coding, characterized in that: include: A continuous laser (1), an optical amplifier (2), a signal generator (3), an erbium-doped fiber amplifier (4), a wavelength division multiplexer (5), a photodetector (6), a data acquisition card (7), a computer (8), and a sensing fiber (9). The continuous laser light output by the continuous laser (1) is converted into pulse light after passing through the optical amplifier (2). The pulse light is amplified by the erbium-doped fiber amplifier (4) and then enters the sensing fiber (9) through the wavelength division multiplexer (5). The Raman backscattered light generated in the sensing fiber (9) is output by the wavelength division multiplexer (5) and then detected by the photodetector (6). The detection signal is collected by the data acquisition card (7) and then sent to the computer (8). The signal generator (3) is used to drive the optical amplifier (2) to perform strong autocorrelation pulse code modulation on the continuous laser output by the continuous laser (1). There are four groups of coding sequences used in the strong autocorrelation pulse code modulation, which are: Among them, U1, W1, U2, and W2 are one of the coding sequences, A k and B k are two code words of length k; A k *A k +B k *B k =2Mδ, where "*" represents the correlation operation, M represents the codeword length, and δ is the impulse function; The computer (8) is used to calculate the temperature information along the sensing optical fiber according to the received single pulse backward Raman scattered light signals corresponding to the four groups of coding sequences.

2. A Raman distributed optical fiber temperature measurement system based on strong autocorrelation pulse coding according to claim 1, characterized in that: The computer (8) calculates the temperature information along the sensing optical fiber using the following calculation formula: Wherein, T represents the temperature to be measured, T0 represents the temperature in the calibration stage, RBS(T0) and RBS(T) represent the equivalent single pulse Raman backscattered light signal intensities in the calibration stage and the measurement stage, respectively.

3. The Raman distributed optical fiber temperature measurement system based on strong autocorrelation pulse coding according to claim 2 is characterized in that: The calculation formula of the equivalent single-pulse Raman backscattered light signal intensity is: Among them, u, w and They are the single pulse Raman backscattered light signals corresponding to the coding sequences U1, W1, U2, and W2, is the convolution operation, h k is the input impulse response.

4. The Raman distributed optical fiber temperature measurement system based on strong autocorrelation pulse coding according to claim 3 is characterized in that: The single pulse Raman backscattered light signal u corresponding to the coding sequence U1, W1, U2, W2, w and The calculation formula is: Among them, RBS'(U1), RBS'(U2), RBS'(W1), RBS'(W1) respectively represent the single pulse Raman backscattered light signals corresponding to the coding sequences U1, W1, U2, W2 received by the photodetector (6), fft represents Fourier transform, ifft represents inverse Fourier transform, and F' represents the result of Fourier transform of the attenuation envelope f.

5. The Raman distributed optical fiber temperature measurement system based on strong autocorrelation pulse coding according to claim 3 is characterized in that: The calculation formula for calculating the measurement position by the computer (8) is: L represents the measurement position, c represents the speed of light in a vacuum, n represents the refractive index of the medium, and t represents the time from the emission of the signal to its return.

6. The Raman distributed optical fiber temperature measurement system based on strong autocorrelation pulse coding according to claim 1 is characterized in that: The wavelength division multiplexer (5) is used to output the Raman backward anti-Stokes scattered light signal generated in the sensing optical fiber (9) and send it to the photoelectric detector (6).

7. The Raman distributed optical fiber temperature measurement system based on strong autocorrelation pulse coding according to claim 1 is characterized in that: The wavelength of the continuous laser (1) is 1550 nm, the photodetector (6) is an avalanche photodetector with a bandwidth of 200 MHz; the sampling rate of the acquisition card is 1 GSa / s; and the sensing optical fiber (9) is a single-mode optical fiber.

8. A Raman distributed optical fiber temperature measurement method based on strong autocorrelation pulse coding, implemented based on the Raman distributed optical fiber temperature measurement system based on strong autocorrelation pulse coding described in claim 1, characterized in that: The following steps are involved: Step 1: In the calibration stage, the temperature in the sensing optical fiber is set to T0, and the optical amplifier (2) is driven by a signal generator (3) to perform strong autocorrelation pulse code modulation on the continuous laser output by the continuous laser (1); The single pulse Raman backscattered light signals corresponding to each coding sequence are received by a photoelectric detector; Step 2: During the measurement phase, the signal generator (3) drives the optical amplifier (2) to perform strong autocorrelation pulse code modulation on the continuous laser output by the continuous laser (1); The single pulse Raman backscattered light signals corresponding to each coding sequence are received by a photoelectric detector; Step 3: Calculate the equivalent single-pulse Raman backscattered light signal intensity according to the single-pulse Raman backscattered light signals corresponding to each coding sequence obtained in the calibration stage and the measurement stage; the calculation formula for the equivalent single-pulse Raman backscattered light signal intensity is: Among them, u, w and They are the single pulse backward Raman anti-Stokes optical signals corresponding to the coding sequences U1, W1, U2, and W2 respectively; is the convolution operation, h k is the input impulse response; Step 4: Calculate the temperature information along the sensing optical fiber according to the equivalent single-pulse Raman backscattered light signal intensity. The calculation formula is: Wherein, T represents the temperature to be measured, T0 represents the temperature in the calibration stage, RBS(T0) and RBS(T) represent the equivalent single pulse Raman backscattered light signal intensities in the calibration stage and the measurement stage, respectively.

9. The Raman distributed optical fiber temperature measurement method based on strong autocorrelation pulse coding according to claim 8, characterized in that: The single pulse Raman backscattered light signal u corresponding to the coding sequence U1, W1, U2, W2, w and The calculation formula is: Among them, RBS'(U1), RBS'(U2), RBS'(W1), RBS'(W1) respectively represent the single pulse Raman backscattered light signals corresponding to the coding sequences U1, W1, U2, W2 received by the photodetector (6), fft represents Fourier transform, ifft represents inverse Fourier transform, and F' represents the result of Fourier transform of the attenuation envelope f.

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