A raman distributed fiber sensing device based on forward and backward joint scattering

Abstract

The application relates to the field of distributed optical fiber sensing, in particular to a Raman distributed optical fiber sensing device based on forward and backward joint scattering, wherein pulse laser emitted by a chaotic pulse light source enters a sensing optical fiber after a first wavelength division multiplexer, spontaneous Raman scattering and Rayleigh scattering occur in the sensing optical fiber, Rayleigh backward scattering light signals and spontaneous Raman backward anti-Stokes scattering signals excited at each point along the sensing optical fiber return to the first wavelength division multiplexer and are detected by a first avalanche photodetector and a second avalanche photodetector respectively, spontaneous Raman forward scattering signals excited at each point along the sensing optical fiber are received by a third avalanche photodetector, and output signals of the three avalanche photodetectors are sent to a computer for calculation of cross-correlation curves after data acquisition cards. The application can improve the spatial resolution of the system and optimize the measurement time of the system.

Description

Technical Field

[0001] This invention relates to the field of distributed optical fiber sensing, specifically a Raman distributed optical fiber sensing device based on combined forward and backward scattering. Background Technology

[0002] Fiber optic sensing technology has become one of the most remarkable and rapidly developing high-tech fields in the world today. Along with communication and computer technologies, it forms the three pillars of the information industry and is an important indicator of contemporary scientific and technological development. Raman distributed fiber optic sensing technology utilizes the Raman scattering signal in an optical fiber as a function of the fiber's temperature to detect temperature changes at different locations along the fiber. It has played a significant role in improving the performance of military weaponry, polar scientific expeditions, and the exploration and development of geothermal resources, powerfully promoting the progress of related scientific research.

[0003] However, due to the principle of optical time-domain reflectometry (OTDR) positioning, traditional Raman distributed fiber optic sensing technology suffers from poor positioning accuracy and its spatial resolution cannot exceed the meter level. Furthermore, due to pulse broadening, the spatial resolution gradually deteriorates with sensing distance, making ultra-long-distance sensing (≥50km) impossible. Existing Raman distributed fiber optic sensing technology has a sensing distance of 10km and a spatial resolution of 1m, which is insufficient to meet the higher performance requirements of fields such as polar scientific research, geothermal resource exploration and development, and nuclear power plant safety monitoring. How to effectively improve the sensing distance of Raman distributed fiber optic sensing systems while maintaining spatial resolution performance is a key scientific and technical issue for improving the system's performance.

[0004] Therefore, it is necessary to improve existing Raman distributed fiber optic sensing devices and methods to overcome the technical bottleneck that existing distributed fiber optic sensing technology cannot achieve long sensing distances while maintaining spatial resolution performance. Summary of the Invention

[0005] In order to overcome the above-mentioned technical bottlenecks in the prior art, the technical problem to be solved by the present invention is to provide a Raman distributed fiber optic sensing device and method based on forward and backward joint scattering, so as to achieve high resolution of the Raman distributed fiber optic sensing system over long sensing distances.

[0006] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: a Raman distributed fiber optic sensing device based on forward and backward joint scattering, comprising: a laser, a semiconductor optical amplifier, an amplified spontaneous emission source, an electro-optic modulator, an optical pulse generator, a first wavelength division multiplexer, a sensing fiber, a first avalanche photodetector, a second avalanche photodetector, a third avalanche photodetector, a data acquisition card, and a computer.

[0007] The laser emits continuous laser light, which is modulated by a semiconductor optical amplifier connected to amplify the spontaneous emission source, generating ASE laser light. The ASE laser light is then modulated into ASE pulsed laser light by an electro-optic modulator driven by an optical pulse generator. After passing through ports a and d of the first wavelength division multiplexer, it enters the sensing fiber. Spontaneous Raman scattering and Rayleigh scattering occur in the sensing fiber. The Rayleigh backscattered light signal and the spontaneous Raman backscattered anti-Stokes scattering signal excited at various points along the sensing fiber return to port d of the first wavelength division multiplexer. The Rayleigh backscattered light signal is output from port b and detected by the first avalanche photodetector, while the spontaneous Raman backscattered anti-Stokes scattering signal is output from port c and detected by the second avalanche photodetector. The spontaneous Raman forward scattering signal excited at various points along the sensing fiber is received by the third avalanche photodetector.

[0008] The output signals of the first avalanche photodetector, the second avalanche photodetector, and the third avalanche photodetector are acquired by the data acquisition card and sent to the computer. The computer uses the Fresnel reflection signal at the end of the Rayleigh backscattered light signal as a reference signal and calculates its cross-correlation curve with the forward and backward anti-Stokes misalignment subtraction signal. The cross-correlation curve is used to demodulate the position and temperature of the temperature variation zone.

[0009] The formula for calculating the cross-correlation curve is:

[0010]

[0011] Where τ represents the delay time, R 1'3 (τ) represents the cross-correlation function between the reference signal and the spontaneous Raman backward anti-Stokes dislocation subtraction signal, R 4'3 (τ) represents the cross-correlation function between the reference signal and the spontaneous Raman forward misalignment subtraction signal, and its expression is:

[0012]

[0013]

[0014] Where t represents time, Φ1'(t) represents the spontaneous Raman backward anti-Stokes misaligned subtraction signal, Φ4'(t) represents the spontaneous Raman forward anti-Stokes misaligned subtraction signal, and Φ3(t-τ) represents the value of the reference signal at time t-τ.

[0015] The calculation formulas for the spontaneous Raman backward anti-Stokes misalignment subtraction signal and the spontaneous Raman forward misalignment subtraction signal are as follows:

[0016] Φ1'(t)=Φ1(t+1)-Φ1(t);

[0017] Φ4'(t)=Φ4(t+1)-Φ4(t);

[0018] Φ1(t+1) and Φ1(t) represent the intensity of the spontaneous Raman backward anti-Stokes light at times t and t+1, respectively, and Φ4(t+1) and Φ4(t) represent the intensity of the spontaneous Raman forward anti-Stokes light at times t and t+1.

[0019] The wavelength of the laser is 1550nm.

[0020] The wavelengths of ports a and b of the first wavelength division multiplexer are 1550nm, the wavelength of port c is 1450nm, and the wavelength of port d is 1450 / 1550nm.

[0021] The Raman distributed fiber optic sensing device based on forward and backward scattering further includes a second wavelength division multiplexer.

[0022] The spontaneous Raman forward scattering signals excited at various points along the sensing fiber by the ASE pulsed laser are filtered by the second multiplexer and then received by the third avalanche photodetector.

[0023] The Raman distributed fiber optic sensing device based on forward and backward scattering further includes an erbium-doped fiber amplifier disposed between the electro-optic modulator and the first wavelength division multiplexer; the ASE pulse laser output from the electro-optic modulator is amplified by the erbium-doped fiber amplifier and then output to the first wavelength division multiplexer.

[0024] The laser (1) is a distributed feedback laser.

[0025] The sensing fiber has a nonlinear parameter greater than 10W. -1 km -1 Nonlinear multimode optical fiber.

[0026] Compared with existing distributed fiber optic sensing devices, the Raman distributed fiber optic sensing device and method based on joint forward and backward scattering proposed in this invention has the following advantages:

[0027] (1) The spatial resolution of the present invention depends on the full width at half maximum (FWHM) of the correlation peak of the cross-correlation curve, which eliminates the problem that the spatial resolution of the traditional Raman distributed fiber optic sensing system is limited by the pulse width. It can improve the spatial resolution of the Raman distributed fiber optic sensing system to the millimeter level over long sensing distances.

[0028] (2) The location and temperature of the temperature change zone can be determined by the correlation peak of the cross-correlation curve, thus optimizing the measurement time of the system. Attached Figure Description

[0029] Figure 1 A schematic diagram of the structure of a Raman distributed fiber optic sensing device based on joint forward and backward scattering provided in an embodiment of the present invention;

[0030] In the diagram: 1: Laser, 2: Semiconductor optical amplifier, 3: Amplified spontaneous emission source, 4: Electro-optic modulator, 5: Optical pulse generator, 6: Erbium-doped fiber amplifier, 7: First wavelength division multiplexer, 8: Sensing fiber, 9: Second wavelength division multiplexer, 10: First avalanche photodetector, 11: Second avalanche photodetector, 12: Third avalanche photodetector, 13: Data acquisition card, 14: Computer. Detailed Implementation

[0031] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are some embodiments of the present invention, but not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0032] Example 1

[0033] like Figure 1 As shown, Embodiment 1 of the present invention provides a Raman distributed fiber optic sensing device based on forward and backward joint scattering, comprising: a laser 1, a semiconductor optical amplifier 2 (SOA), an amplified spontaneous emission source 3 (ASE), an electro-optic modulator 4, an optical pulse generator 5, a first wavelength division multiplexer 7, a sensing fiber 8, a first avalanche photodetector 10, a second avalanche photodetector 11, a third avalanche photodetector 12, a data acquisition card 13, and a computer 14.

[0034] The laser 1 emits continuous laser light, which is modulated by a semiconductor optical amplifier 2 connected to amplify spontaneous emission light source 3 to generate ASE laser. The ASE laser is then modulated into ASE pulse laser by an electro-optic modulator 4 driven by an optical pulse generator 5. After passing through ports a and d of the first wavelength division multiplexer 7, it enters the sensing fiber 8. Spontaneous Raman scattering and Rayleigh scattering occur in the sensing fiber 8. The Rayleigh backscattered light signal and the spontaneous Raman backscattered anti-Stokes scattering signal excited at various points along the sensing fiber 8 return to port d of the first wavelength division multiplexer 7. The Rayleigh backscattered light signal is output from port b and detected by the first avalanche photodetector 10. The spontaneous Raman backscattered anti-Stokes scattering signal is output from port c and detected by the second avalanche photodetector 11. The spontaneous Raman forward scattering signal excited at various points along the sensing fiber 8 is received by the third avalanche photodetector 12.

[0035] The output signals of the first avalanche photodetector 10, the second avalanche photodetector 11, and the third avalanche photodetector 12 are acquired by the data acquisition card 13 and sent to the computer 14. The computer 14 uses the Fresnel reflection signal at the end of the Rayleigh backscattered light signal as a reference signal to calculate the cross-correlation curve. The cross-correlation curve is used to demodulate the position and temperature of the temperature variation zone.

[0036] Specifically, such as Figure 1 As shown, the output of laser 1 is connected to port a of semiconductor optical amplifier 2, the output of amplified spontaneous emission source 3 is connected to port b of semiconductor optical amplifier 2, port c of semiconductor optical amplifier 2 is connected to port a of electro-optic modulator 4, port b of electro-optic modulator 4 is connected to the output of optical pulse generator 5, port c of electro-optic modulator 4 is connected to the input of erbium-doped fiber amplifier 6, and the output of erbium-doped fiber amplifier 6 is connected to port a of first wavelength division multiplexer 7. Ports a and b of semiconductor optical amplifier are inputs, and port c is the output, with wavelengths of 1550 nm at ports a, b, and c. Ports a and b of electro-optic modulator 4 are inputs, and port c is the output, with wavelengths of 1550 nm at ports a, b, and c.

[0037] Specifically, in this embodiment, the wavelength of the laser 1 is 1550 nm. It can be a narrow-linewidth distributed feedback laser with a power of approximately 20 mW. The amplified spontaneous emission source 3 has advantages such as high output power, wide spectral linewidth, low polarization degree, high power stability, and good average wavelength stability, with a spectral width reaching 50 nm. The stable continuous laser emitted by the distributed feedback laser is modulated by the laser emitted by the semiconductor optical amplifier 2 and the amplified spontaneous emission source 3 to produce an ASE laser with a high extinction ratio. This ASE laser is then modulated into an ASE pulsed laser by the optical pulse generator 5 and the electro-optic modulator 4. The ASE laser exhibits random fluctuation characteristics and noise-like properties.

[0038] In this process, the semiconductor optical amplifier 2 modulates the laser input to the laser 1 into an ASE laser with a high extinction ratio under the modulation of the amplified spontaneous emission source 3. The optical pulse generator 5 emits a 1550nm optical pulse, and the electro-optic modulator 4 transforms the input continuous ASE laser into an ASE pulse laser with a higher extinction ratio.

[0039] Specifically, in this embodiment, the data acquisition card 13 is a high-speed data acquisition card. The sensing fiber 8 has a nonlinear parameter greater than 10W. -1 km -1 Nonlinear multimode optical fiber.

[0040] Specifically, in this embodiment, the wavelengths of ports a and b of the first wavelength division multiplexer 7 are 1550nm, the wavelength of port c is 1450nm, and the wavelength of port d is 1450 / 1550nm.

[0041] Furthermore, this embodiment of a Raman distributed fiber optic sensing device based on joint forward and backward scattering further includes an erbium-doped fiber amplifier 6 disposed between the electro-optic modulator 4 and the first wavelength division multiplexer 7; the ASE pulsed laser output from the electro-optic modulator 4 is amplified by the erbium-doped fiber amplifier 6 before being output to the first wavelength division multiplexer 7. The erbium-doped fiber amplifier 6 can further amplify the ASE pulsed laser output from the electro-optic modulator to meet the power requirements of the measurement.

[0042] Furthermore, this embodiment of a Raman distributed fiber optic sensing device based on combined forward and backward scattering also includes a second wavelength division multiplexer 9. The spontaneous Raman forward scattering signals excited at various points along the sensing fiber 8 are output from the end of the sensing fiber 8, filtered by the second multiplexer 9, and then received by the third avalanche photodetector 12. The second multiplexer 9 can also be replaced by other filtering devices. The input wavelength of the second wavelength division multiplexer 9 is 1450 / 1550 nm, and the output wavelength connected to the third avalanche photodetector 12 is 1450 nm. Through the second wavelength division multiplexer, the 1450 nm spontaneous Raman forward scattering signal in the sensing fiber 8 can be separated from the original 1550 nm ASE pulsed laser.

[0043] The principle of distributed temperature demodulation of this invention is described below.

[0044] In a Raman distributed fiber optic sensing device based on combined forward and backward scattering according to an embodiment of the present invention, the position of the fiber propagation L is used as a reference point to acquire the Raman backscattering signal, forward scattering signal, and Rayleigh backscattering signal generated in the sensing fiber. The 1550nm laser emitted by the laser 1 is converted into an ASE pulse laser with random temporal fluctuations and a high extinction ratio after passing through the semiconductor optical amplifier 2 and the electro-optic modulator 4. Then, it enters the sensing fiber 8 after passing through the first wavelength division multiplexer 7, where spontaneous Raman scattering and Rayleigh scattering occur at various points along the entire sensing fiber 8. During this process, the ASE pulsed laser simultaneously excites spontaneous Raman backscattering, spontaneous Raman forward scattering, and spontaneous Rayleigh backscattering signals. The 1450nm spontaneous Raman backscattering anti-Stokes signal excited at various points along the sensing fiber 8 returns to the first wavelength division multiplexer 7 and is output from its c port, where it is detected by the second avalanche photodetector 11, and the signal intensity is recorded as Φ1(t). The 1550nm Rayleigh backscattering signal returns to the first wavelength division multiplexer 7 and is output from its b port, where it is detected by the first avalanche photodetector, and the signal intensity is recorded as Φ2(t). The Fresnel reflection signal at the end of the 1550nm Rayleigh backscattering signal Φ2(t) is used as a reference signal, and its signal intensity is recorded as Φ3(t). The 1450nm spontaneous Raman forward scattering signal is output along the end of the sensing fiber 8 and is detected by the third avalanche photodetector 12, and the signal intensity is recorded as Φ4(t).

[0045] In a Raman distributed fiber optic sensing system, the signal intensity at each sampling point is the superposition of light intensity information over the entire pulse width. Therefore, to extract the temperature information at each location point, the scattered signal needs to be subtracted by a misalignment. By subtracting the data from the previous time point from the data from the later time point, the spontaneous Raman backward anti-Stokes misalignment subtraction signal Φ1'(t) can be constructed, and its expression is as follows:

[0046] Φ1'(t)=Φ1(t+1)-Φ1(t); (1)

[0047] Where Φ1(t+1) and Φ1(t) represent the intensity of the spontaneous Raman backward anti-Stokes light at times t+1 and t, respectively. Φ1'(t) represents the spontaneous Raman backward anti-Stokes dislocation subtraction signal.

[0048] Cross-correlating the reference signal with the spontaneous Raman backward anti-Stokes misalignment subtraction signal yields:

[0049]

[0050] Where Φ3(t-τ) represents the value of the reference signal at time t-τ, τ represents the delay time, and R 1'3(τ) represents the cross-correlation function between the reference signal and the spontaneous Raman backward anti-Stokes misaligned subtraction signal, and T represents the upper and lower limits of integration.

[0051] Simultaneously, the spontaneous Raman forward scattering signal with a wavelength of 1450 nm excited by the ASE pulsed laser is detected by the third avalanche photodetector 12, and the signal intensity is recorded as Φ4(t). Similarly, the spontaneous Raman forward misalignment subtraction signal Φ4'(t) is constructed, and its expression is as follows:

[0052] Φ4'(t)=Φ4(t+1)-Φ4(t); (3)

[0053] Wherein, Φ4'(t) represents the spontaneous Raman forward misalignment subtraction signal, and Φ4(t+1) and Φ4(t) represent the intensity of the spontaneous Raman forward anti-Stokes light at times t+1 and t, respectively.

[0054] Cross-correlating the reference signal with the spontaneous Raman forward misalignment subtraction signal yields the following:

[0055]

[0056] Among them, R 4'3 (τ) represents the cross-correlation function between the reference signal and the spontaneous Raman forward misalignment subtraction signal.

[0057] Taking the geometric mean of the above results yields:

[0058]

[0059] Among them, R Com (τ) represents the cross-correlation curve. The cross-correlation curve Rt is used to... Com The correlation peak of (τ) can determine the location and temperature of the temperature change zone.

[0060] In this embodiment, the Fresnel reflection signal Φ3(t) at the end of the Rayleigh backscattered light signal with a wavelength of 1550nm has a very high similarity to the original ASE pulse signal. The original ASE pulse signal is a pulse signal with random amplitude characteristics and noise-like characteristics modulated by an amplified spontaneous emission source ASE. Therefore, when it is selected as a reference signal, when there is no temperature difference between adjacent points in the sensing fiber, the signal magnitude after correlation with the spontaneous Raman back-stokes misalignment subtraction signal and the spontaneous Raman forward misalignment subtraction signal is close to 0. When there is a temperature difference between adjacent points in the sensing fiber, the correlated signal exhibits ASE-based noise-like characteristics. Then, by obtaining the delay time of the correlation peak, the precise location of the abrupt signal can be obtained. The spatial resolution of this embodiment depends on the full width at half maximum (FWHM) of the correlation peak of the cross-correlation curve, which is determined by the bandwidth of the modulated pulsed laser.

[0061] In summary, this invention provides a Raman distributed fiber optic sensing device based on forward and backward joint scattering. It utilizes a laser, a semiconductor optical amplifier, an amplified spontaneous emission source, an electro-optic modulator, and an optical pulse generator to generate a high extinction ratio ASE pulsed laser. Then, using the Fresnel reflection signal at the end of the Rayleigh backscattered light signal as a reference signal, its cross-correlation function with the forward and backward anti-Stokes misalignment subtraction signals is calculated. By demodulating the position and temperature of the temperature variation zone through the cross-correlation curve, the measurement time of the system is optimized. Furthermore, the spatial resolution of this invention depends on the full width at half maximum (FWHM) of the correlation peak of the cross-correlation curve, eliminating the problem of spatial resolution being limited by pulse width in traditional Raman distributed fiber optic sensing systems. This allows the spatial resolution of Raman distributed fiber optic sensing systems to be improved to the millimeter level over long sensing distances.

[0062] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A Raman distributed fiber optic sensing device based on joint forward and backward scattering, characterized in that, include: Laser (1), semiconductor optical amplifier (2), amplified spontaneous emission source (3), electro-optic modulator (4), optical pulse generator (5), first wavelength division multiplexer (7), sensing fiber (8), first avalanche photodetector (10), second avalanche photodetector (11), third avalanche photodetector (12), data acquisition card (13), computer (14). The laser (1) emits continuous laser light, which is modulated by a semiconductor optical amplifier (2) connected to amplify spontaneous emission light source (3) to generate ASE laser. The ASE laser is modulated into ASE pulse laser by an electro-optic modulator (4) driven by an optical pulse generator (5). Then, it enters the sensing fiber (8) through the a and d ports of the first wavelength division multiplexer (7). Spontaneous Raman scattering and Rayleigh scattering occur in the sensing fiber (8). The Rayleigh backscattered light signal and spontaneous Raman backscattered anti-Stokes scattering signal excited at each point along the sensing fiber (8) return to the d port of the first wavelength division multiplexer (7). The Rayleigh backscattered light signal is output from its b port and detected by the first avalanche photodetector (10). The spontaneous Raman backscattered anti-Stokes scattering signal is output from its c port and detected by the second avalanche photodetector (11). The spontaneous Raman forward scattering signal excited at each point along the sensing fiber (8) is received by the third avalanche photodetector (12). The output signals of the first avalanche photodetector (10), the second avalanche photodetector (11), and the third avalanche photodetector (12) are acquired by the data acquisition card (13) and sent to the computer (14). The computer (14) uses the Fresnel reflection signal at the end of the Rayleigh backscattered light signal as a reference signal and calculates its cross-correlation curve with the forward and backward anti-Stokes misalignment subtraction signal. The cross-correlation curve is used to demodulate the position and temperature of the temperature change zone.

2. The Raman distributed fiber optic sensing device based on joint forward and backward scattering according to claim 1, characterized in that, The formula for calculating the cross-correlation curve is: Where τ represents the delay time, R 1'3 (τ) represents the cross-correlation function between the reference signal and the spontaneous Raman backward anti-Stokes dislocation subtraction signal, R 4'3 (τ) represents the cross-correlation function between the reference signal and the spontaneous Raman forward misalignment subtraction signal, and its expression is: Where t represents time, Φ1'(t) represents the spontaneous Raman backward anti-Stokes misaligned subtraction signal, Φ4'(t) represents the spontaneous Raman forward anti-Stokes misaligned subtraction signal, and Φ3(t-τ) represents the value of the reference signal at time t-τ.

3. The Raman distributed fiber optic sensing device based on joint forward and backward scattering according to claim 1, characterized in that, The calculation formulas for the spontaneous Raman backward anti-Stokes misalignment subtraction signal and the spontaneous Raman forward misalignment subtraction signal are as follows: Φ1'(t)=Φ1(t+1)-Φ1(t); Φ4'(t)=Φ4(t+1)-Φ4(t); Φ1(t+1) and Φ1(t) represent the intensity of the spontaneous Raman backward anti-Stokes light at times t and t+1, respectively, and Φ4(t+1) and Φ4(t) represent the intensity of the spontaneous Raman forward anti-Stokes light at times t and t+1.

4. The Raman distributed fiber optic sensing device based on joint forward and backward scattering according to claim 1, characterized in that, The wavelength of the laser (1) is 1550nm.

5. A Raman distributed fiber optic sensing device based on joint forward and backward scattering according to claim 4, characterized in that, The wavelengths of ports a and b of the first wavelength division multiplexer (7) are 1550nm, the wavelength of port c is 1450nm, and the wavelength of port d is 1450 / 1550nm.

6. The Raman distributed fiber optic sensing device based on joint forward and backward scattering according to claim 1, characterized in that, It also includes a second wavelength division multiplexer (9); The spontaneous Raman forward scattering signals generated by the ASE pulsed laser at various points along the sensing fiber (8) are filtered by the second multiplexer (9) and then received by the third avalanche photodetector (12).

7. A Raman distributed fiber optic sensing device based on joint forward and backward scattering according to claim 1, characterized in that, It also includes an erbium-doped fiber amplifier (6) disposed between the electro-optic modulator (4) and the first wavelength division multiplexer (7); the ASE pulse laser output by the electro-optic modulator (4) is amplified by the erbium-doped fiber amplifier (6) and then output to the first wavelength division multiplexer (7).

8. A Raman distributed fiber optic sensing device based on joint forward and backward scattering according to claim 1, characterized in that, The laser (1) is a distributed feedback laser.

9. A Raman distributed fiber optic sensing device based on joint forward and backward scattering according to claim 1, characterized in that, The sensing fiber (8) has a nonlinear parameter greater than 10W. -1 km -1 Nonlinear multimode optical fiber.

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