Raman distributed optical fiber sensing device and method based on LFM signal FrFT

Abstract

The invention relates to the technical field of distributed optical fiber sensing, and discloses a Raman distributed optical fiber sensing device and method based on FrFT of an LFM signal, and the method comprises the following steps: driving a pulse light modulator through the LFM signal after p-order FrFT, and enabling the pulse light modulator to output an LFM pulse laser signal to a sensing optical fiber; collecting Raman backscattering signal intensity data at an L position in the sensing optical fiber; performing pulse compression on the acquired Raman backscattering signal intensity data by using (1-p)-order FrFT to obtain an equivalent Raman backscattering signal; and calculating temperature information along the sensing optical fiber according to the equivalent Raman backscattering signal. According to the method, higher signal-to-noise ratio and spatial resolution can be realized by performing fractional Fourier transform on the LFM signal.

Description

Technical Field

[0001] The present invention relates to the field of distributed optical fiber sensing technology, and in particular to a Raman distributed optical fiber sensing device and method based on LFM signal FrFT transform, which achieves higher signal-to-noise ratio and spatial resolution by performing fractional Fourier transform (FrFT) on the LFM signal. Background Art

[0002] Raman distributed fiber optic sensing systems can continuously measure distributed temperature characteristics along the sensing fiber. In this system, the ambient temperature along the sensing fiber modulates the intensity of the Raman scattered light within the fiber. By collecting this Raman scattered light, which carries temperature information, the system can obtain distributed temperature information along the sensing fiber. Raman distributed fiber optic sensing systems offer advantages such as strong environmental adaptability, immunity to electromagnetic interference, a wide detection range, and high temperature accuracy. Therefore, they are widely used in temperature safety monitoring applications such as coal mines, oil and gas pipelines, bridges, and buildings.

[0003] In Raman distributed fiber-optic sensing systems, spatial resolution is a crucial technical specification, reflecting the minimum length over which temperature changes in the fiber can be detected. Signal-to-noise ratio (SNR) is a key factor influencing spatial resolution. The SNR is related to the energy of the injected pump pulse. Increasing the pulse power can effectively improve the SNR, but this is limited by nonlinear effects such as modulation instability. Another approach to improving the SNR is to increase the pulse duration, but this reduces spatial resolution. Distributed optical amplification can overcome these limitations, using Raman amplification, Brillouin amplification, or a combination of both to compensate for fiber losses. These approaches have successfully extended sensing distances to over 100 km. However, they require high-power pump sources and introduce additional noise. Another approach utilizes linear frequency modulated (LFM) pulses and matched filters. This exploits the pulse compression properties of LFM to achieve high spatial resolution with long pulse durations. However, a key issue with this approach is the relatively low peak-to-sidelobe ratio (PSLR) in the matched filter, which can cause crosstalk. The PSLR is typically improved by applying a window function to the matched filter during demodulation. However, due to filter mismatch, this results in a loss of SNR and reduced spatial resolution.

[0004] Based on this, it is necessary to invent a new Raman distributed fiber optic sensing system to solve the problem that the spatial resolution of the existing Raman distributed fiber optic sensing system is affected by the low signal-to-noise ratio, thereby improving the spatial resolution. Summary of the Invention

[0005] In order to solve the problem that the spatial resolution of existing Raman distributed fiber optic sensing systems is limited by the low signal-to-noise ratio, resulting in low spatial resolution, the present invention proposes a Raman distributed fiber optic sensing device and method based on LFM signal FrFT transform, which applies fractional Fourier transform to the generation and pulse compression of LFM signals to achieve higher signal-to-noise ratio and spatial resolution.

[0006] In order to solve the above technical problems, the technical solution adopted by the present invention is: a Raman distributed optical fiber sensing method based on LFM signal FrFT transformation, comprising the following steps:

[0007] S1. Build a Raman distributed fiber optic sensing device and drive the pulse light modulator with the LFM signal after the p-order FrFT transformation to output the LFM pulse laser signal to the sensing fiber;

[0008] S2, calibration stage: measure the Raman backscattering signal intensity I(L, T0) at room temperature T0; use 1-p order FrFT to perform pulse compression on the Raman backscattering signal intensity I(L, T0) at room temperature T0 to obtain the equivalent Raman backscattering signal R(L, T0) at room temperature;

[0009] S3, measurement phase: collecting Raman backscatter signal intensity data I(L,T) at various positions in the sensing fiber; where L is the position in the sensing fiber;

[0010] S4. Using a 1-p order FrFT to perform pulse compression on the collected Raman backscattering signal intensity data I(L, T) to obtain an equivalent Raman backscattering signal R(L, T);

[0011] S5. Calculate the temperature information along the sensing optical fiber according to the equivalent Raman backscattering signal R(L, T) and the equivalent Raman backscattering signal R(L, T0) at room temperature.

[0012] In step S1, the LFM signal after the p-order FrFT transformation is:

[0013]

[0014] Among them, X p (u) represents the LFM signal after the p-order FrFT transformation, A is the amplitude of the original one-dimensional signal, α represents the rotation angle of the time-frequency plane, α=pπ / 2, and u represents the frequency.

[0015] The collected Raman backscattered signal is a Raman backscattered anti-Stokes signal.

[0016] In step S4, the collected Raman backscatter signal intensity data I(L) is pulse compressed using a (1-p) order FrFT to obtain an equivalent Raman backscatter signal R(L, T) using the formula:

[0017]

[0018] Where I(L) represents the intensity of the Raman backscattered signal collected at the sensing fiber L position, K 1―p (t,u) represents the kernel function of order 1-p, and the expression is:

[0019]

[0020] Where α' represents the rotation angle of the time-frequency plane when the order is 1-p, α' = (1-p)π / 2, u represents frequency, and t represents time.

[0021] In step S5, the temperature information along the sensing optical fiber is calculated according to the equivalent Raman backscattering signal R(t):

[0022]

[0023] Where T represents the demodulated sensing fiber temperature, h is the Planck constant, k is the Boltzmann constant, and Δν is the Raman frequency shift.

[0024] In addition, the present invention also provides a Raman distributed optical fiber sensing device based on LFM signal FrFT transformation, including a laser, a pulse light modulator, an LFM signal generator, a wavelength division multiplexer, a sensing optical fiber, a photodetector, a data acquisition card and a computer;

[0025] The LFM signal generator is used to emit an LFM signal after a p-order FrFT transformation to drive a pulse light modulator. The laser output by the laser is converted into an LFM light pulse signal after passing through the pulse light modulator, and then is incident on the sensing optical fiber after passing through a wavelength division multiplexer. The Raman scattered light generated in the sensing optical fiber is filtered by the wavelength division multiplexer and detected by a photodetector, and then collected by a data acquisition card and sent to the computer. The computer is used to perform a 1-p-order FrFT transformation on the detected Raman scattered light signal to obtain an equivalent Raman backscattering signal, and demodulate the equivalent Raman backscattering signal to obtain a temperature signal, wherein 0<p<1.

[0026] The Raman distributed optical fiber sensing device based on FrFT transformation of LFM signals also includes a pulsed erbium-doped fiber amplifier, which is arranged between the pulse light modulator and the wavelength division multiplexer and is used to amplify the power of the LFM optical pulse signal modulated by the pulse light modulator.

[0027] The LFM signal after the p-order FrFT transformation is:

[0028]

[0029] Among them, X p (u) represents the LFM signal after the p-order FrFT transformation, A is the amplitude of the original one-dimensional signal, α represents the rotation angle of the time-frequency plane, α=pπ / 2, and u represents the frequency.

[0030] Among them, p=0.3.

[0031] In the Raman distributed optical fiber sensing device based on the FrFT transform of the LFM signal, the computer performs a 1-p order FrFT transform on the detected Raman scattered light signal to obtain the specific formula of the equivalent Raman backscattering signal R(L, t):

[0032]

[0033] Wherein, I(L) represents the intensity of the Raman backscattered signal collected at the position of the sensing fiber L;

[0034] The specific formula for obtaining the temperature signal by demodulating the equivalent Raman backscattered signal is:

[0035]

[0036] Where T represents the demodulated sensing fiber temperature, h is the Planck constant, k is the Boltzmann constant, Δν is the Raman frequency shift, R(L, T) and R(L, T0) represent the equivalent Raman backscattering signal and the equivalent Raman backscattering signal at room temperature, respectively.

[0037] Compared with the prior art, the present invention has the following beneficial effects:

[0038] The present invention provides a Raman distributed optical fiber sensing device and method based on the FrFT transform of an LFM signal. The p-order fractional Fourier transform (FrFT) is applied to the generation and pulse compression of the LFM signal. The FrFT is a generalization of the traditional Fourier transform (FFT) and introduces rotation in the time-frequency domain. The collected scattered signal is then pulse compressed using the (1-p)-order FrFT. By extending the decomposition basis function of the FrFT from a single-frequency sinusoidal signal to the LFM signal, a fully compressed LFM pulse with a high PSLR and a narrow full width at half maximum (FWHM) is obtained. Therefore, the present invention can achieve a higher signal-to-noise ratio and spatial resolution while maintaining constant power. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1A schematic structural diagram of a Raman distributed optical fiber sensing device based on FrFT transformation of LFM signals provided by an embodiment of the present invention;

[0040] Figure 2 Schematic diagram of a DC signal before FrFT transformation in an embodiment of the present invention;

[0041] Figure 3 Graph showing the LFM pulse signal after 0.3-order FrFT in an embodiment of the present invention;

[0042] Figure 4 Graph showing the equivalent Raman backscattering signal after 0.7-order FrFT in an embodiment of the present invention;

[0043] In the figure: 1- semiconductor laser, 2- pulse light modulator, 3- arbitrary waveform generator, 4- pulsed erbium-doped fiber amplifier, 5- wavelength division multiplexer, 6- sensing fiber, 7- photodetector, 8- data acquisition card, 9- computer. DETAILED DESCRIPTION

[0044] In order to make the purpose, 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 part of the embodiments of the present invention, not all the embodiments; based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0045] Example 1

[0046] like Figure 1 As shown, the first embodiment of the present invention provides a Raman distributed optical fiber sensing device based on LFM signal FrFT transformation, including a laser 1, a pulse light modulator 2, an LFM signal generator 3, a wavelength division multiplexer 5, a sensing optical fiber 6, a photodetector 7, a data acquisition card 8 and a computer 9;

[0047] The LFM signal generator 3 is used to emit an LFM signal after p-order FrFT transformation to drive the pulse light modulator 2. The laser output by the laser 1 is converted into an LFM light pulse signal after passing through the pulse light modulator 2, and then is incident on the sensing optical fiber 6 after passing through the wavelength division multiplexer 5. The Raman scattered light generated in the sensing optical fiber 6 is filtered by the wavelength division multiplexer 5 and detected by the photodetector 7. It is then collected by the data acquisition card 8 and sent to the computer 9. The computer is used to perform a 1-p-order FrFT transformation on the detected Raman scattered light signal to obtain an equivalent Raman backscattering signal, and demodulate the equivalent Raman backscattering signal to obtain a temperature signal, where 0<p<1.

[0048] Furthermore, the Raman distributed optical fiber sensing device based on FrFT transformation of LFM signals in this embodiment also includes a pulsed erbium-doped fiber amplifier 4, which is arranged between the pulse optical modulator 2 and the wavelength division multiplexer 5, and is used to amplify the power of the LFM optical pulse signal modulated by the pulse optical modulator 2.

[0049] Furthermore, in this embodiment, the LFM signal generator 3 is specifically an arbitrary waveform signal generator. Specifically, in this embodiment, p=0.3.

[0050] Specifically, in this embodiment, laser 1 is a semiconductor laser operating at a wavelength of 1550 nm. The signal detected by photodetector 7 is Raman backscattered anti-Stokes light. Raman backscattered anti-Stokes light with a wavelength of 1450 nm generated in the sensing fiber is filtered by a wavelength division multiplexer and then detected by photodetector 7. A data acquisition card 8 collects the detection signal from photodetector 7 and transmits it to computer 9.

[0051] The computer is used to perform 1-p order FrFT transformation on multiple groups of Raman backscattering signals, and then perform calculation and processing based on the transformed data to locate and demodulate the temperature mutation point information along the optical fiber.

[0052] The sensing and demodulation principle of the present invention is introduced below.

[0053] 1. Generation of LFM Signal

[0054] The p-order fractional Fourier transform signal X of the one-dimensional signal x(t) p (u) can be defined from the perspective of integral transformation as:

[0055]

[0056] Among them F p represents the p-order fractional Fourier transform operator, t represents the time variable, u represents the frequency variable, and the kernel function K p The expression of (t,u) is:

[0057]

[0058] Where α represents the rotation angle of the time-frequency plane when the order is p, α=pπ / 2, A α is the coefficient related to α, p is the order of FrFT, and n is a positive integer.

[0059] In this embodiment, the additivity of FrFT orders is utilized to generate the LFM pulse signal X using a p-order FrFT of a DC signal x(t)=A. p (u), therefore, it can be expressed as:

[0060]

[0061] Simplifying, we can get:

[0062]

[0063] Where A represents the signal amplitude, such as Figure 2 As shown, this is a schematic diagram of the DC signal used. Figure 3 This is the LFM pulse signal diagram after 0.3-order FrFT.

[0064] 2. Raman backscattering signal intensity processing

[0065] (1) Collection and processing of Raman backscattered signals.

[0066] In temperature demodulation, the Raman backscattered anti-Stokes signal intensity at the sensing fiber L is:

[0067]

[0068] Where P is the incident power of the pulsed laser, K a Denotes the coefficient related to the Raman anti-Stokes backscattering cross section, λ a is the wavelength of the Raman anti-Stokes scattering signal, α0, α as are the loss coefficients of incident light and anti-Stokes light per unit length in the sensing fiber, L is the position of the sensing fiber, and R as (T) is the temperature modulation function of the anti-Stokes scattered light, and its expression is:

[0069]

[0070] Where Δν is the Raman frequency shift, h is the Planck constant, k is the Boltzmann constant, and T is the temperature of the sensing fiber. Therefore, the Raman backscattered anti-Stokes signal I is obtained by measurement. as After (L), the temperature T can be obtained by demodulation using equations (5) to (6).

[0071] In this embodiment, the LFM pulse signal X is generated by a p-order FrFT using a DC signal x(t)=A. p (u), then when the temperature is T, the collected Raman backscattered anti-Stokes signal intensity I(L,T) can actually be expressed as:

[0072]

[0073] in, represents the convolution operation, I as(L) represents the backscattered Raman anti-Stokes signal at position L of the sensing fiber under normal LFM pulse input conditions.

[0074] Therefore, by using the 1-p order FrFT to compress the collected backscattered Raman anti-Stokes signal intensity I(L,T), the equivalent Raman backscattered signal R(L,T) can be obtained, which is expressed as follows:

[0075]

[0076] Among them, K 1―p (t,u) represents the kernel function of order 1-p.

[0077] Assuming the temperature value at room temperature is T0, the Raman backscattering anti-Stokes signal measured at room temperature is I(L,T0), then the corresponding equivalent Raman backscattering signal at room temperature is:

[0078]

[0079] Due to the backscattered Raman anti-Stokes signal I as (L) is modulated by temperature T, and the temperature modulation function is R as (T); Therefore, the collected Raman backscattered anti-Stokes signal I(L,T) and the equivalent Raman backscattered signal R(L,T) are also modulated by the temperature T. Therefore, we have:

[0080]

[0081] Among them, R as (T) and R as (T0) represents the temperature modulation function value at temperature T and temperature T0, respectively, and R(L, T) and R(L, T0) represent the temperature modulation function value at temperature T and temperature T0, respectively. Therefore, the temperature can be demodulated using the equivalent backscattered signal R(L, T). Specifically, the present invention provides a method for compressing the backscattered Raman anti-Stokes signal intensity I(L) generated by the LFM pulse signal through a 1-p order FrFT. The resulting equivalent Raman backscattered signal R(L, T) is used to demodulate the temperature using an anti-Stokes single-path demodulation method.

[0082] Specifically, substituting formula (6) into formula (10) yields:

[0083]

[0084] The simplified calculation formula for the temperature T along the optical fiber is:

[0085]

[0086] Where h is Planck's constant, k is Boltzmann's constant, and Δν is the Raman frequency shift.

[0087] In this embodiment, the spatial resolution of the device is determined by the FWHM of the main lobe of the equivalent Raman backscatter signal R(L, T). Theoretically, the pulse signal is sensed through the p-order FrFT, and the collected Raman backscatter signal intensity is pulse compressed through the 1-p-order FrFT. The two FrFTs are equivalent to the direct FFT of the DC signal, which solves the crosstalk caused by the relatively low PSLR. Therefore, the technical solution of this embodiment can be expected to obtain a fully compressed LFM pulse with high PSLR and narrow FWHM. Figure 4 As shown, the equivalent pulse after 0.7-order FrFT compression. Since the spatial resolution of the device is determined by the FWHM of the equivalent Raman backscattered signal, the embodiment of the present invention can achieve a higher signal-to-noise ratio and spatial resolution.

[0088] In this embodiment of the present invention, an LFM signal is generated using the p-order FrFT of a DC signal using Equation (4). The collected backscattered Raman anti-Stokes signal I(L,T) is then compressed using the 1-p-order FrFT using Equation (8), resulting in a fully compressed LFM pulse with high PSLR and narrow FWHM. Finally, the temperature T along the fiber can be obtained using Equation (12).

[0089] In summary, in the embodiments of the present invention, the FrFT is applied to the generation and pulse compression of LFM signals. The FrFT is used instead of the matched filter to obtain a fully compressed LFM pulse with a high PSLR and a narrow FWHM. This solves the crosstalk caused by the relatively low PSLR and achieves a higher signal-to-noise ratio and spatial resolution.

[0090] Example 2

[0091] A second embodiment of the present invention provides a Raman distributed optical fiber sensing method based on FrFT transformation of an LFM signal, comprising the following steps:

[0092] S1. Build a Raman distributed fiber optic sensing device and drive the pulse light modulator 2 with the LFM signal after the p-order FrFT transformation, so that it outputs the LFM pulse laser signal to the sensing fiber.

[0093] In the step S1, the expression of the LFM signal after the p-order FrFT transformation is the above formula (4).

[0094] S2. Calibration stage: measure the Raman backscattering signal intensity data I(L, T0) at room temperature T0; use the 1-p order FrFT to perform pulse compression on the Raman backscattering signal intensity I(L, T0) at room temperature T0 to obtain the equivalent Raman backscattering signal R(L, T0) at room temperature.

[0095] The formula for the equivalent Raman backscattering signal R(L, T0) at room temperature is:

[0096]

[0097] Among them, K 1―p (t,u) represents the kernel function of order 1-p.

[0098] Specifically, the expression of the kernel function with order 1-p is:

[0099]

[0100] in, α' represents the rotation angle of the time-frequency plane when the order is 1-p, α' = (1-p)π / 2.

[0101] S3, measurement phase: collecting Raman backscattering signal intensity data I(L,T) at various positions in the sensing optical fiber;

[0102] S4. Using a 1-p order FrFT to perform pulse compression on the collected Raman backscattering signal intensity data I(L, T) to obtain an equivalent Raman backscattering signal R(L, T);

[0103] In step S4, the collected Raman backscatter signal intensity data I(L, T) is pulse compressed using a (1-p) order FrFT to obtain an equivalent Raman backscatter signal R(L, T) using the formula:

[0104]

[0105] Where I(L,T) represents the intensity of the Raman backscattered signal collected at the sensing fiber L position.

[0106] S5. Calculate the temperature information along the sensing optical fiber according to the measured equivalent Raman backscattering signal R(L, T) and the equivalent Raman backscattering signal R(L, T0) at room temperature.

[0107] In step S5, the temperature information along the sensing optical fiber is calculated according to the equivalent Raman backscattering signal R(L, T) and R(L, T0):

[0108]

[0109] Wherein, T represents the demodulated sensing fiber temperature, T0 represents room temperature, h is Planck's constant, k is Boltzmann's constant, and Δν is the Raman frequency shift.

[0110] 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 above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above 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 sensing method based on LFM signal FrFT transform, characterized in that: The following steps are involved: S1, build a Raman distributed optical fiber sensing device, and drive the pulse light modulator (2) with the LFM signal after the p-order FrFT transformation, so that it outputs the LFM pulse laser signal to the sensing optical fiber; Where 0<p<1; S2, calibration stage: measure the Raman backscattering signal intensity I(L, T0) at room temperature T0; use 1-p order FrFT to perform pulse compression on the Raman backscattering signal intensity I(L, T0) at room temperature T0 to obtain the equivalent Raman backscattering signal R(L, T0) at room temperature; S3, measurement phase: collecting Raman backscatter signal intensity data I(L,T) at various positions in the sensing fiber; where L is the position in the sensing fiber; S4. Using a 1-p order FrFT to perform pulse compression on the collected Raman backscattering signal intensity data I(L, T) to obtain an equivalent Raman backscattering signal R(L, T); S5. Calculate the temperature information along the sensing optical fiber according to the equivalent Raman backscattering signal R(L, T) and the equivalent Raman backscattering signal R(L, T0) at room temperature.

2. The Raman distributed optical fiber sensing method based on LFM signal FrFT transformation according to claim 1, characterized in that: In step S1, the LFM signal after the p-order FrFT transformation is: Among them, X p (u) represents the LFM signal after the p-order FrFT transformation, A is the amplitude of the original one-dimensional signal, α represents the rotation angle of the time-frequency plane, α=pπ / 2, and u represents the frequency.

3. The Raman distributed optical fiber sensing method based on LFM signal FrFT transformation according to claim 2, characterized in that: The collected Raman backscattered signal is a Raman backscattered anti-Stokes signal.

4. The Raman distributed optical fiber sensing method based on LFM signal FrFT transformation according to claim 1, characterized in that: In step S4, the collected Raman backscatter signal intensity data I(L) is pulse compressed using a (1-p) order FrFT to obtain an equivalent Raman backscatter signal R(L, T) using the formula: Where I(L) represents the intensity of the Raman backscattered signal collected at the sensing fiber L position, K 1―p (t,u) represents the kernel function of order 1-p, and the expression is: Where α' represents the rotation angle of the time-frequency plane when the order is 1-p, α' = (1-p)π / 2, u represents frequency, and t represents time.

5. The Raman distributed optical fiber sensing method based on LFM signal FrFT transformation according to claim 1, characterized in that: In step S5, the temperature information along the sensing optical fiber is calculated using the following formula: Where T represents the demodulated sensing fiber temperature, h is the Planck constant, k is the Boltzmann constant, and Δν is the Raman frequency shift.

6. A Raman distributed optical fiber sensing device based on LFM signal FrFT transformation, characterized in that: The invention comprises a laser (1), a pulse light modulator (2), an LFM signal generator (3), a wavelength division multiplexer (5), a sensing optical fiber (6), a photodetector (7), a data acquisition card (8) and a computer (9); The LFM signal generator (3) is used to emit an LFM signal after p-order FrFT transformation to drive the pulse light modulator (2). The laser light output by the laser (1) is converted into an LFM light pulse signal after passing through the pulse light modulator (2), and then is incident on the sensing optical fiber (6) after passing through the wavelength division multiplexer (5). The Raman scattered light generated in the sensing optical fiber (6) is filtered by the wavelength division multiplexer (5) and detected by the photoelectric detector (7). The Raman scattered light is then collected by the data acquisition card (8) and sent to the computer (9). The computer is used to perform 1-p-order FrFT transformation on the detected Raman scattered light signal to obtain an equivalent Raman backscattering signal, and demodulate the equivalent Raman backscattering signal to obtain a temperature signal, wherein 0<p<1.

7. The Raman distributed optical fiber sensing device based on LFM signal FrFT transformation according to claim 6, characterized in that: It also includes a pulsed erbium-doped fiber amplifier (4), which is arranged between the pulsed light modulator (2) and the wavelength division multiplexer (5) and is used to amplify the power of the LFM optical pulse signal modulated and generated by the pulsed light modulator (2).

8. The Raman distributed optical fiber sensing device based on LFM signal FrFT transformation according to claim 6, characterized in that: The LFM signal after the p-order FrFT transformation is: Among them, X p (u) represents the LFM signal after the p-order FrFT transformation, A is the amplitude of the original one-dimensional signal, α represents the rotation angle of the time-frequency plane, α=pπ / 2, and u represents the frequency.

9. The Raman distributed optical fiber sensing device based on LFM signal FrFT transformation according to claim 6, characterized in that: p＝0.3。 10. The Raman distributed optical fiber sensing device based on LFM signal FrFT transformation according to claim 6, characterized in that: The computer performs a 1-p order FrFT transform on the detected Raman scattered light signal to obtain the specific formula of the equivalent Raman backscattering signal R(L, t): Wherein, I(L) represents the intensity of the Raman backscattered signal collected at the position L of the sensing fiber; The specific formula for obtaining the temperature signal by demodulating the equivalent Raman backscattered signal is: Where T represents the demodulated sensing fiber temperature, h is the Planck constant, k is the Boltzmann constant, Δν is the Raman frequency shift, R(L, T) and R(L, T0) represent the equivalent Raman backscattering signal and the equivalent Raman backscattering signal at room temperature, respectively.

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