Raman distributed optical fiber temperature measurement system and method with high spatial resolution

Abstract

The invention relates to the technical field of distributed optical fiber sensing, in particular to a Raman distributed optical fiber sensing device and method with high spatial resolution performance, and the method comprises the following steps: pulse laser is divided into two beams, one beam is used as sensing light to enter a sensing optical fiber, and the other beam is used as sensing light to enter the sensing optical fiber; receiving a Raman backscattering signal phi output from the sensing optical fiber through a detector, and receiving the other beam as reference light through the detector to obtain a discrete pulse signal; constructing a square matrix X according to the discrete pulse signals; calculating a temperature coefficient through the constructed square matrix X and a Raman backscattering signal phi; and calculating the temperature along the sensing optical fiber according to the temperature coefficient. According to the invention, the influence of the pulse width on the system spatial resolution performance under the traditional system can be eliminated, and high-resolution temperature measurement is realized.

Description

Technical Field

[0001] The present invention relates to the technical field of distributed optical fiber sensing, and specifically to a Raman distributed optical fiber sensing device and method with high spatial resolution performance, which are mainly oriented to new application fields such as two-dimensional and three-dimensional temperature mapping of complex electronic devices, particle detectors, and aerospace instruments. Background Art

[0002] The Raman distributed optical fiber temperature sensing technology is widely used in occasions such as crude oil product pipeline leakage detection, high-voltage cable overload detection, and fire detection in large warehouses due to its characteristics of corrosion resistance, strong electromagnetic interference resistance, small system volume, and low maintenance and use costs.

[0003] Spatial resolution, as an important performance index of the system, measures the minimum fiber length that the sensing system can resolve when measuring the temperature field of the sensing optical fiber. Since the system realizes the positioning of optical signals based on the optical time domain reflectometry principle, the ideal spatial resolution that the traditional Raman distributed optical fiber temperature sensing system can achieve is the spatial distance corresponding to half of the pulse width, resulting in the spatial resolution of most current Raman distributed optical fiber sensing systems being limited to the meter level and unable to be improved.

[0004] In recent years, new precision manufacturing industries such as the production of complex electronic devices have developed rapidly. The distributed optical fiber sensing technology is convenient for laying in a narrow space and can be applied to environments with strong corrosion and strong electromagnetic interference, which helps the existing precision manufacturing industry to achieve real-time temperature monitoring with high spatial resolution performance. However, since the Raman distributed optical fiber temperature sensing system uses the optical time domain reflectometry principle to realize the positioning of signals, most existing Raman distributed optical fiber temperature sensing systems can only monitor temperature changes with a temperature change distance > 1m.

[0005] Temperature is an important physical quantity in the processing environment of precision manufacturing. The accurate monitoring of temperature helps to precisely control the state of materials and the adjustment of processing techniques during the manufacturing process. Tiny temperature changes will have a huge impact on the manufacturing results. Based on this, it is necessary to propose a Raman distributed optical fiber sensing device and method with high spatial resolution performance for precision manufacturing to solve the technical bottleneck that the existing distributed optical fiber sensing technology cannot balance long sensing distance and high spatial resolution performance. Summary of the Invention

[0006] In order to solve the above technical bottleneck, the present invention proposes a Raman distributed optical fiber sensing device and method with high spatial resolution performance to achieve high spatial resolution temperature real-time monitoring of the distributed optical fiber sensing system.

[0007] To solve the above technical problems, the technical solution adopted by the present invention is as follows: A Raman distributed optical fiber temperature measurement method with high spatial resolution, comprising the following steps:

[0008] Step 1: Divide the pulsed laser into two beams, one beam as the sensing light is incident on the sensing optical fiber, and the Raman backscattering signal Φ output from the sensing optical fiber is received by a detector, and the other beam as the reference light is received by the detector to obtain a discrete pulse signal;

[0009] Step 2: Construct a square matrix X according to the discrete pulse signal; the construction method of the square matrix X is as follows:

[0010]

[0011] Wherein, X(i, i−b) represents the element in the i-th row and the (i−b)-th column of the square matrix X, X(i, i−b+1) represents the element in the i-th row and the (i−b + 1)-th column of the square matrix X, laser(b + 1) and laser(b) represent the values of the (b + 1)-th and b-th data points of the discrete pulse signal, z represents the length of the discrete pulse signal array, c represents the length of the Raman backscattering signal Φ; d represents the number of rows and columns of the square matrix X, d = c - z + 1; i, b are positive integers;

[0012] Step 3: Calculate the temperature coefficient through the constructed square matrix X and the Raman backscattering signal Φ;

[0013] Step 4: Calculate the temperature along the sensing optical fiber according to the temperature coefficient.

[0014] The calculation formula for the temperature coefficient is:

[0015] R = X ―1 × Φ;

[0016] Wherein, R represents the temperature coefficient, X ―1 represents the inverse matrix of the square matrix X.

[0017] The calculation formula for the temperature along the sensing optical fiber is:

[0018]

[0019] Wherein, R represents the temperature coefficient, Δv is the Raman frequency shift, h is the Planck constant, k is the Boltzmann constant, and T is the temperature of the sensing optical fiber.

[0020] In addition, the present invention also provides a Raman distributed optical fiber temperature measurement system with high spatial resolution for implementing the temperature measurement method, including: a pulsed laser source, a coupler, an erbium-doped fiber amplifier, a bandwidth filter, a sensing optical fiber, a first photodetector, a second photodetector, a data acquisition card, and a computer; the pulsed laser output by the pulsed laser source is divided into two beams of probe light and reference light by the coupler, wherein the probe light is amplified by the erbium-doped fiber amplifier and then enters the sensing optical fiber through the bandwidth filter, and the Raman backscattering signal output from the sensing optical fiber is received by the first photodetector after passing through the bandwidth filter; the reference light is received by the second photodetector; the electrical signal output terminals of the first photodetector and the second photodetector are connected to the data acquisition card, and the data acquisition card is used to send the collected signals to the computer, and the computer is used to calculate the temperature along the sensing optical fiber.

[0021] The pulsed laser source includes a continuous laser, a semiconductor optical modulator, and a digital delay pulse sequence generator. Among them, the continuous laser emitted by the continuous laser is modulated by the semiconductor optical modulator driven by the digital delay pulse sequence generator to output a pulsed laser with a fixed pulse width.

[0022] The Raman distributed optical fiber temperature measurement system with high spatial resolution further includes an attenuator, and the attenuator is arranged in front of the second photodetector for attenuating the reference light entering the second photodetector.

[0023] The coupler is a coupler with a splitting ratio of 99:1, where 99 parts are used as the probe light and 1 part is used as the reference light.

[0024] The first photodetector and the second photodetector are avalanche photodetectors.

[0025] The digital delay pulse sequence generator is connected to the data acquisition card for providing a synchronization signal to the data acquisition card.

[0026] The bandwidth filter is an optical circulator.

[0027] The present invention has the following beneficial effects compared with the prior art:

[0028] (1) The present invention proposes a Raman distributed optical fiber sensing device and method with high spatial resolution performance. By synchronously collecting the Raman backscattering signal and the discrete pulse signal corresponding to the reference light through the data acquisition card, and then using the computer to construct a square matrix through the collected discrete pulse signals, and performing deconvolution processing on the square matrix and the Raman backscattering signal to obtain the temperature coefficient, and then demodulating the temperature along the optical fiber, it is possible to realize the temperature monitoring along the optical fiber direction that takes into account both long-distance sensing and high spatial resolution performance.

[0029] (2) The present invention overcomes the problem of deterioration of the system spatial resolution caused by using pulse signals with a large pulse width in the case of long distances, can eliminate the influence of the pulse width on the system spatial resolution performance in the traditional system, and can improve the temperature measurement accuracy of the distributed optical fiber sensing system to <10 cm at long distances. Description of the Drawings

[0030] Figure 1 It is a schematic flow chart of a Raman distributed optical fiber temperature measurement method with high spatial resolution provided by an embodiment of the present invention;

[0031] Figure 2 It is a schematic structural diagram of a Raman distributed optical fiber temperature measurement system with high spatial resolution provided by the second embodiment of the present invention;

[0032] Figure 3 It is the demodulated temperature curve of the present invention under different signal-to-noise ratio conditions.

[0033] In the figure: 1: Digital delay pulse sequence generator, 2: Semiconductor optical modulator, 3: Coupler, 4: Erbium-doped fiber amplifier, 5: Bandwidth filter, 6: Sensing optical fiber, 7: First photodetector, 8: Attenuator, 9: Second photodetector, 10: Data acquisition card, 11: Computer, 12: Laser. Detailed Embodiments

[0034] 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, but not 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.

[0035] Embodiment 1

[0036] As Figure 1 shown, an embodiment of the present invention provides a Raman distributed optical fiber temperature measurement method with high spatial resolution, including the following steps:

[0037] Step 1: Divide the pulsed laser into two beams. One beam is used as the sensing light and is incident on the sensing optical fiber, and the Raman backscattering signal Φ output from the sensing optical fiber is received by the detector. The other beam is used as the reference light and the discrete pulse signal is received by the detector. Then, the Raman backscattering signal and the signal of the reference light are collected by the high-speed data acquisition card. In this embodiment, the Raman backscattering signal can be the Raman back anti-Stokes scattering signal.

[0038] Step 2: Construct a square matrix X according to the discrete pulse signal; the construction method of the square matrix X is:

[0039]

[0040] Among them, X(i, i−b) represents the element in the i-th row and the (i−b)-th column of the square matrix X, X(i, i−b) represents the element in the i-th row and the (i−b + 1)-th column of the square matrix X, laser(b + 1) and laser(b) represent the values of the (b + 1)-th and b-th data points of the discrete pulse signal, z represents the length of the discrete pulse signal array, i and b are positive integers, and c represents the length of the Raman backscattering signal Φ. Among them, d represents the number of rows and columns of the square matrix X, and d = c−z + 1.

[0041] Step 3: Calculate the temperature coefficient through the constructed square matrix X and the Raman backscattering signal Φ.

[0042] Specifically, the calculation formula for the temperature coefficient is:

[0043] R = X ―1 × Φ; (2)

[0044] Among them, R represents the temperature coefficient, and X ―1 represents the inverse matrix of the square matrix X.

[0045] Step 4: Calculate the temperature along the sensing optical fiber according to the temperature coefficient.

[0046] Specifically, the calculation formula for the temperature along the sensing optical fiber is:

[0047]

[0048] Among them, R represents the temperature coefficient, Δv is the Raman frequency shift, h is Planck's constant, k is Boltzmann's constant, and T is the temperature of the sensing optical fiber.

[0049] The measurement principle of the present invention will be introduced below.

[0050] In Raman distributed optical fiber sensing applications, the Raman backscattering signal intensity at a single-point position obtained by a high-speed data acquisition card is the superposition point of the intensity signals excited by the pulsed laser in the entire spatial length of the sensing optical fiber. Under this physical principle, when the pulse width of the laser signal used is τ, and the pulsed signal collected by the high-speed data card is a discrete time-series signal composed of m data points, when the sampling rate of the high-speed acquisition card is f, the following relationship exists:

[0051] m = τf (4)

[0052] Let I i and I j be the pulse signal intensities at the starting point and the ending point of the pulse respectively, and j−i = m, then the Raman backscattering signal intensity at a certain point n collected by the high-speed data acquisition card can be expressed as;

[0053]

[0054] Among them, R n―a represents the temperature coefficient at the positions of the first a points at a certain point n of the optical fiber, and I a is the pulse signal intensity corresponding to the a-th point in the pulse signal, and I a can be obtained from the discrete pulse signal of the collected reference light, and this signal is a discrete signal intensity sequence.

[0055] In addition, the expression of the temperature coefficient is as follows:

[0056]

[0057] Among them, Δv is the Raman frequency shift, h is Planck's constant, k is Boltzmann's constant, and T is the temperature of the sensing optical fiber.

[0058] In this embodiment, a square matrix X is constructed according to the discrete pulse signal of the reference light collected by the high-speed data acquisition card, and it satisfies that the Raman backscattering signal at a certain point position collected in the experiment is the product of the constructed square matrix X and the discrete matrix R of the temperature coefficient along the optical fiber direction, that is:

[0059] Φ = X × R (7)

[0060] Among them, assuming that the length of the discrete pulse signal array Laser is z and the length of the Raman backscattering signal Φ collected by the acquisition card is c, the construction method of the square matrix X is:

[0061]

[0062] Among them, z is the intensity of the discrete pulse signal array Laser, c is the length of the Raman backscattering signal collected by the acquisition card, i and b are positive integers, and d represents the number of rows and columns of the square matrix X, d = c - z + 1.

[0063] Since the inverse matrix of a square matrix can be directly obtained, therefore, only by multiplying the inverse matrix of the square matrix X by the discrete Raman backscattering signal intensity matrix can the original temperature coefficient be obtained, that is, the above formula (3).

[0064] Embodiment 2

[0065] Such as Figure 2As shown in the figure, Embodiment 2 of the present invention provides a Raman distributed optical fiber temperature measurement system with high spatial resolution for implementing the temperature measurement method described in Embodiment 1, including: a pulsed laser source, a coupler 3, an erbium-doped fiber amplifier 4, a bandwidth filter 5, a sensing optical fiber 6, a first photodetector 7, a second photodetector 9, a data acquisition card 10, and a computer 11; the pulsed laser output by the pulsed laser source is divided into two beams of probe light and reference light by the coupler 3, wherein the probe light is amplified by the erbium-doped fiber amplifier 4 and then enters the sensing optical fiber 6 through the bandwidth filter 5, and the Raman backscattering signal output from the sensing optical fiber 6 is received by the first photodetector 7 after passing through the bandwidth filter 5; the reference light is received by the second photodetector 9; the electrical signal output terminals of the first photodetector 7 and the second photodetector 9 are connected to the data acquisition card 10, and the data acquisition card is used to send the collected signals to the computer 11, and the computer 11 is used to calculate the temperature along the sensing optical fiber.

[0066] Specifically, in this embodiment, the pulsed laser source includes a continuous laser 12, a semiconductor optical modulator 2, and a digital delay pulse sequence generator 1. Among them, the continuous laser emitted by the continuous laser 12 is modulated by the semiconductor optical modulator 2 driven by the digital delay pulse sequence generator 1 to output a pulsed laser with a fixed pulse width.

[0067] Further, a Raman distributed optical fiber temperature measurement system with high spatial resolution in this embodiment further includes an attenuator 8, and the attenuator 8 is arranged in front of the second photodetector 9 for attenuating the reference light entering the second photodetector 9.

[0068] Further, in this embodiment, the coupler 3 is a coupler with a splitting ratio of 99:1, where 99 parts are used as the probe light and 1 part is used as the reference light.

[0069] Further, in this embodiment, the first photodetector 7 and the second photodetector 9 are avalanche photodetectors. The data acquisition card 10 is a high-speed data acquisition card.

[0070] Further, in this embodiment, the digital delay pulse sequence generator 1 is connected to the data acquisition card 10 for providing a synchronization signal to the data acquisition card 10.

[0071] Further, in this embodiment, the bandwidth filter 5 is an optical circulator.

[0072] Specifically, in this embodiment, the computer is used to construct a square matrix X according to the discrete pulse signal, and is also used to calculate the temperature coefficient according to the constructed square matrix X and the Raman backscattering signal Φ, and to demodulate the temperature along the sensing optical fiber according to the calculated temperature coefficient.

[0073] As Figure 3As shown in the figure, it is a schematic diagram of the temperature curve obtained by using the deconvolution demodulation method of the present invention under different signal-to-noise ratio conditions. Among them, the ideal signal is not affected by noise and signal superposition, so it will not cause rising edges and falling edges in the temperature change region signal, nor will it lead to signal broadening and a decrease in spatial resolution; the actual signal is not affected by noise, but due to signal superposition caused by applying the optical time domain reflectometry principle for positioning, rising edges and falling edges appear in the signal at the temperature change region, ultimately resulting in signal broadening and a decrease in spatial resolution; the deconvolution result is the temperature curve obtained by using the demodulation method of the present invention under the influence of a certain amount of noise. It can be seen from the figure that after the signal-to-noise ratio is higher than 20 dB, the demodulation result of the present invention is basically consistent with the ideal signal, overcoming the problem that rising edges and falling edges appear in the temperature change region signal caused by signal superposition, ultimately leading to signal broadening and a decrease in spatial resolution. Therefore, the present invention can achieve a high spatial resolution.

[0074] 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 them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some or all of the technical features; and 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 method with high spatial resolution, characterized in that: The following steps are involved: Step 1: Split the pulsed laser into two beams, one beam is incident on the sensing optical fiber as sensing light, and the Raman backscattering signal Φ output from the sensing optical fiber is received by the detector, and the other beam is received by the detector as reference light to obtain a discrete pulse signal; Step 2: construct a square matrix X according to the discrete pulse signal; the construction method of the square matrix X is: Wherein, X(i, i―b) represents the element of the i-th row and the ib-th column of the square matrix X, X(i, i―b) represents the element of the i-th row and the i-b+1-th column of the square matrix X, laser(b+1) and laser(b) represent the values ​​of the b+1-th and b-th data points of the discrete pulse signal, z represents the length of the discrete pulse signal array, c represents the length of the Raman backscattering signal Φ; d represents the number of rows and columns of the square matrix X, d=c-z+1; i and b are positive integers; Step 3: Calculate the temperature coefficient using the constructed square matrix X and the Raman backscattering signal Φ; Step 4: Calculate the temperature along the sensing optical fiber based on the temperature coefficient.

2. A Raman distributed optical fiber temperature measurement method with high spatial resolution according to claim 1, characterized in that: The temperature coefficient is calculated as follows: R=X ―1 ×Φ; Where R represents the temperature coefficient, X ―1 Represents the inverse matrix of the square matrix X.

3. The Raman distributed optical fiber temperature measurement method with high spatial resolution according to claim 1, characterized in that: The calculation formula for the temperature along the sensing optical fiber is: Where R is the temperature coefficient, Δv is the Raman frequency shift, h is the Planck constant, k is the Boltzmann constant, and T is the sensing fiber temperature.

4. A Raman distributed optical fiber temperature measurement system with high spatial resolution, characterized in that: A method for implementing the method according to any one of claims 1 to 3, comprising: a pulse laser source, a coupler (3), an erbium-doped fiber amplifier (4), a bandwidth filter (5), a sensing fiber (6), a first photodetector (7), a second photodetector (9), a data acquisition card (10), and a computer (11); the pulse laser output by the pulse laser source is divided into two beams of detection light and reference light by the coupler (3); the detection light is amplified by the erbium-doped fiber amplifier (4) and then enters the sensing fiber (6) through the bandwidth filter (5); the Raman backscattering signal output from the sensing fiber (6) is received by the first photodetector (7) after passing through the bandwidth filter (5); the reference light is received by the second photodetector (9); the electrical signal output ends of the first photodetector (7) and the second photodetector (9) are connected to the data acquisition card (10); the data acquisition card is used to send the collected signals to the computer (11); the computer (11) is used to calculate the temperature along the sensing fiber.

5. The Raman distributed optical fiber temperature measurement system with high spatial resolution according to claim 4, characterized in that: The pulse laser source comprises a continuous laser (12), a semiconductor light modulator (2) and a digital time-delay pulse sequence generator (1), wherein the continuous laser light emitted by the continuous laser (12) is modulated by the semiconductor light modulator (2) driven by the digital time-delay pulse sequence generator (1) to output pulse laser light with a fixed pulse width.

6. The Raman distributed optical fiber temperature measurement system with high spatial resolution according to claim 4, characterized in that: The invention also comprises an attenuator (8), which is arranged before the second photodetector (9) and is used for attenuating the reference light entering the second photodetector (9).

7. The Raman distributed optical fiber temperature measurement system with high spatial resolution according to claim 4, characterized in that: The coupler (3) is a coupler with a splitting ratio of 99:1, wherein the 99 part is used as detection light and the 1 part is used as reference light.

8. The Raman distributed optical fiber temperature measurement system with high spatial resolution according to claim 4, characterized in that: The first photodetector (7) and the second photodetector (9) are avalanche photodetectors.

9. The Raman distributed optical fiber temperature measurement system with high spatial resolution according to claim 5, characterized in that: The digital delayed pulse sequence generator (1) is connected to a data acquisition card (10) and is used to provide a synchronization signal to the data acquisition card (10).

10. The Raman distributed optical fiber temperature measurement system with high spatial resolution according to claim 5, characterized in that: The bandwidth filter (5) is an optical circulator.

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