Raman distributed sensing device and method based on sinusoidal modulation light

Abstract

The invention relates to the field of distributed optical fiber sensing, in particular to a Raman distributed sensing device and method based on sinusoidal modulation light. In the device, an electro-optical modulator is driven by a sinusoidal signal output by a sinusoidal signal generator to carry out sinusoidal modulation on continuous laser output by a continuous laser, and the modulated laser is amplified by an optical amplifier and then enters a sensing optical fiber through a wavelength division multiplexer; a Raman backward anti-Stokes scattering signal generated by each point in the sensing optical fiber is output by the wavelength division multiplexer and then is detected by the photoelectric detector; and after being received and recorded by the oscilloscope, a detection signal output by the photoelectric detector is sent to the calculation unit for calculation to obtain position information and temperature information of the temperature change area. The problem that the spatial resolution is limited by the pulse width in a traditional Raman distributed optical fiber sensing system is solved, and the sensing distance can be greatly increased on the basis that the spatial resolution of the system is not reduced.

Description

Technical Field

[0001] The present invention relates to the field of distributed optical fiber sensing, and in particular to a Raman distributed sensing device and method based on sinusoidal modulated light. Background Art

[0002] Raman distributed fiber optic sensing technology uses optical fiber as a sensing element and transmission medium, and uses back Raman scattering information to detect temperature field changes at different locations along the sensing fiber. Due to its advantages such as continuous temperature measurement, high safety, corrosion resistance, and anti-electromagnetic interference, it has become an international key research field. In the field of large-scale infrastructure structural health monitoring, such as tunnels, power cables, gas pipelines, dams and other major infrastructure projects, temperature safety monitoring has great social needs and application prospects.

[0003] For Raman optical time-domain reflectometry technology, the existing distributed optical fiber sensing technology at home and abroad has the technical bottleneck that the system sensing distance and spatial resolution cannot be taken into account at the same time, resulting in insufficient effective sensing points, poor positioning accuracy, and the spatial resolution cannot exceed the meter level. At the same time, due to the pulse broadening phenomenon, the spatial resolution gradually deteriorates with the sensing distance, and ultra-long distance sensing (≥50km) cannot be achieved. The sensing distance of the existing Raman distributed optical fiber sensing technology is 10km, and the spatial resolution is 1m, which is difficult to meet the higher performance requirements in the fields of polar scientific research, geothermal resource exploration and development, and nuclear power plant safety monitoring. In the current improvement of Raman optical time-domain reflectometry technology, the introduction of chaotic optical sensing can break through the problem that the sensing distance and spatial resolution cannot be taken into account at the same time, but in the experiment, its sensing distance is limited, and the chaotic light state is unstable, and its reliability is difficult to guarantee. In order to improve the spatial resolution, reducing the pulse width will cause the sensing distance to deteriorate sharply. Therefore, effectively improving the sensing distance of the Raman distributed optical fiber sensing system while taking into account the spatial resolution performance is the key scientific problem and technical bottleneck for improving the performance of the system.

[0004] In summary, the above-mentioned technical bottlenecks greatly limit the application of Raman distributed fiber optic sensing technology. Therefore, it is necessary to improve the existing Raman distributed fiber optic sensing device and temperature demodulation method to solve the technical bottleneck of the existing Raman distributed fiber optic sensing system that the system sensing distance and spatial resolution cannot be taken into account at the same time, thereby improving the system's sensing performance such as sensing distance and spatial resolution. Summary of the invention

[0005] In order to break through the technical bottleneck of the traditional Raman distributed fiber optic sensing system that cannot take into account both spatial resolution and sensing distance, the present invention proposes a Raman distributed sensing device and method based on sinusoidal modulated light to meet the requirements of Raman distributed fiber optic sensing technology for long distance and high spatial resolution.

[0006] In order to solve the above technical problems, the technical solution adopted by the present invention is: a Raman distributed sensing device based on sinusoidal modulated light, comprising: a continuous laser, an electro-optical modulator, an optical amplifier, a wavelength division multiplexer, a sensing optical fiber, a photodetector, a sinusoidal signal generator, and an oscilloscope; the electro-optical modulator is used to sinusoidally modulate the continuous laser output by the continuous laser under the drive of the sinusoidal signal output by the sinusoidal signal generator, the modulated laser is amplified by the optical amplifier, and then incident on the sensing optical fiber through the wavelength division multiplexer, the Raman backward anti-Stokes scattering signal generated at each point in the sensing optical fiber is output by the wavelength division multiplexer, and then detected by the photodetector; the detection signal output by the photodetector is received and recorded by the oscilloscope, and then sent to the calculation unit to calculate the position information and temperature information of the temperature change zone.

[0007] The continuous laser is a semiconductor laser, the optical amplifier is an erbium-doped fiber amplifier, the sinusoidal signal generator is an arbitrary waveform generator, the photodetector is an avalanche photodetector, and the frequency of the sinusoidal signal output by the sinusoidal signal generator is 100 MHz to 10 GHz.

[0008] The Raman distributed sensing device based on sinusoidal modulated light also includes a pulse generator, the output end of which is connected to the sinusoidal signal generator and the oscilloscope, and is used to output a pulse trigger signal to simultaneously trigger the sinusoidal signal generator and the oscilloscope.

[0009] The wavelength of the continuous laser is centered at 1550nm, and the wavelength of the Raman backscattered anti-Stokes signal is 1450nm; the wavelength of the port of the wavelength division multiplexer connected to the optical amplifier is 1550nm, the wavelength of the port connected to the sensing optical fiber is 1550nm&1450nm, and the wavelength of the port connected to the photodetector is 1450nm.

[0010] In addition, the present invention also provides a Raman distributed sensing method based on sinusoidal modulated light, which is implemented based on the above device and includes the following steps:

[0011] Step 1: Control the sinusoidal signal generator to output N cycles of sinusoidal signals, and receive the Raman backward anti-Stokes scattering signal output from the sensing optical fiber through an oscilloscope; wherein the value of N is 5 to 100;

[0012] Step 2: Repeat step 1, use an oscilloscope to obtain the Raman backscattering anti-Stokes signal multiple times and perform cumulative averaging to obtain the Raman backscattering anti-Stokes average signal excited in the entire sensing optical fiber;

[0013] Step 3: Determine the starting position and length of the temperature change zone according to the positions of the rising zone and the oscillation zone in the temperature change zone in the average signal of the Raman back anti-Stokes scattering excited in the entire sensing optical fiber;

[0014] Step 4: Calculate the temperature information of the temperature change zone according to the signal intensity of any period in the oscillation zone of the Raman backscattering anti-Stokes average signal.

[0015] In step 3, the temperature information calculation formula of the temperature change zone is:

[0016]

[0017] Where T represents the temperature in the temperature change zone, φ a (T,L) and φ a0 (T, L) are the spontaneous Raman backscattering anti-Stokes scattering signal intensities of the same period in the “oscillation zone” phase measured during measurement and calibration, respectively; T0 is the temperature during calibration, h is the Planck constant, Δν is the Raman frequency shift, and k is the Boltzmann constant.

[0018] The step 4 also includes the step of performing autocorrelation operation on the average signal of Raman backward anti-Stokes scattering excited in the entire section of the sensing optical fiber (5) to obtain an autocorrelation coefficient, and then extracting the average signal of spontaneous Raman backward anti-Stokes scattering excited by the single-cycle modulation signal according to the periodicity of the autocorrelation coefficient.

[0019] The calculation formula of the autocorrelation coefficient is:

[0020]

[0021] Where x[n] and x[n+m] represent the nth and n+mth data points of the original signal, respectively, m represents the delay, R xx [m] represents the autocorrelation coefficient.

[0022] In step 3, the calculation formula for the length of the temperature change zone is:

[0023] L0=Z1-Z0;

[0024] Among them, L0 represents the length of the temperature change zone, Z1 represents the starting point of the oscillation zone, and Z0 represents the starting point of the rising zone.

[0025] The step 1 also includes the following steps: adjusting the period of the sinusoidal signal output by the sinusoidal signal generator so that the corresponding spatial scale l0 satisfies the following conditions: l0≤L0 and N·l0>L0; wherein L0 represents the length of the temperature change zone.

[0026] Compared with the existing Raman distributed optical fiber sensing device, the Raman distributed sensing device and method based on sinusoidal modulated light proposed in the present invention have the following beneficial effects:

[0027] (1) The present invention performs sinusoidal intensity modulation on a continuous light source and utilizes the Raman backscattering signal generated when the modulated light is transmitted in the optical fiber to demodulate the position signal and temperature information of the temperature change zone. This eliminates the problem that the spatial resolution in the traditional Raman distributed optical fiber sensing system is limited by the pulse width. As long as the spatial scale corresponding to a single cycle of the modulation signal is less than or equal to the length of the temperature change zone, the position and temperature information of the temperature change zone can be measured.

[0028] (2) When ensuring that the spatial scale of the modulated optical signal within a single cycle is less than or equal to the length of the temperature change zone, the optical power entering the optical fiber can be increased by increasing the number of cycles of the modulated optical signal. Under the premise that stimulated Raman scattering does not occur, the sensing distance can be greatly improved without reducing the spatial resolution of the system.

[0029] (3) Within the allowable modulation range of the electro-optic modulator, by increasing the modulation signal frequency and the modulation period, the spatial scale of the single-cycle modulated light can be shortened without reducing the input optical power, thereby further improving the spatial resolution without affecting the sensing distance. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 A schematic structural diagram of a Raman distributed sensing device based on sinusoidal modulated light provided by an embodiment of the present invention;

[0031] Figure 2 Schematic diagram of Raman backward anti-Stokes scattering curve when the spatial scale of single-cycle modulated light is equal to the length of the temperature change zone; the horizontal axis is the distance and the vertical axis is the signal intensity;

[0032] Figure 3 Schematic diagram of Raman backward anti-Stokes scattering curve when the spatial scale of single-cycle modulated light is smaller than the length of the temperature change zone; the horizontal axis in the figure is distance and the vertical axis is signal intensity.

[0033] In the figure: 1: semiconductor laser, 2: electro-optic modulator, 3: optical amplifier, 4: wavelength division multiplexer, 5: sensing optical fiber, 6: oscilloscope, 7: photodetector, 8: sinusoidal signal generator, 9: pulse generator. DETAILED DESCRIPTION

[0034] 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, rather than 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.

[0035] Embodiment 1

[0036] like Figure 1 As shown, the first embodiment of the present invention provides a Raman distributed sensing device based on sinusoidal modulated light, including: a continuous laser 1, an electro-optical modulator 2, an optical amplifier 3, a wavelength division multiplexer 4, a sensing optical fiber 5, a photodetector 7, a sinusoidal signal generator 8, and an oscilloscope 6; the electro-optical modulator 2 is used to perform sinusoidal modulation on the continuous laser output by the continuous laser 1 under the drive of the sinusoidal signal output by the sinusoidal signal generator 8, the modulated laser is amplified by the optical amplifier 3, and then incident on the sensing optical fiber 5 through the wavelength division multiplexer 4, the Raman backward anti-Stokes scattering signal generated at each point in the sensing optical fiber is output by the wavelength division multiplexer 4, and then detected by the photodetector 7; the detection signal output by the photodetector 7 is received and recorded by the oscilloscope 6, and then sent to the calculation unit to calculate the position information and temperature information of the temperature change zone.

[0037] Specifically, in this embodiment, the continuous laser 1 is a semiconductor laser, the central wavelength of the continuous laser 1 is 1550nm, and the power is 50mW; the optical amplifier 3 is an erbium-doped fiber amplifier, and the maximum gain is 37dB. The sinusoidal signal generator 8 is an arbitrary waveform generator, the photodetector 7 is an avalanche photodetector, and the frequency of the sinusoidal signal output by the sinusoidal signal generator 8 is 100MHz to 10GHz. The sensing fiber 5 is a nonlinear parameter greater than 10W. -1 km -1 The core diameter of the nonlinear multimode optical fiber is 62.5μm.

[0038] Specifically, in this embodiment, the wavelength of the Raman backscattered anti-Stokes signal is 1450nm, the wavelength of the port of the wavelength division multiplexer 4 connected to the optical amplifier 3 is 1550nm, the wavelength of the port connected to the sensing optical fiber 5 is 1550nm&1450nm, and the wavelength of the port connected to the photodetector 7 is 1450nm.

[0039] Furthermore, a Raman distributed sensing device based on sinusoidal modulated light in this embodiment also includes a pulse generator 9, the output end of which is connected to the sinusoidal signal generator 8 and the oscilloscope 6, for outputting a pulse trigger signal to simultaneously trigger the sinusoidal signal generator 8 and the oscilloscope 6.

[0040] Specifically, in this embodiment, the output end of the continuous laser 1 is connected to the a port of the electro-optic modulator 2, the a port of the optical amplifier 3 is connected to the b port of the electro-optic modulator 2, the b port of the optical amplifier 3 is connected to the a port of the wavelength division multiplexer 4, the b port of the wavelength division multiplexer 4 is connected to the sensing optical fiber 5, the c port of the wavelength division multiplexer 4 is connected to the a port of the photodetector 7, the b port of the photodetector 7 and the b port of the pulse generator 9 are respectively connected to the a port and the b port of the oscilloscope 6, the a port of the pulse generator 9 is connected to the a port of the sine signal generator 8, and the b port of the sine signal generator 8 is connected to the c port of the electro-optic modulator 2. Among them, the a port of the electro-optic modulator 2 is the optical input end, the c port is the radio frequency input end, and the b port is the optical output end, and the wavelengths of the a port and the b port are both 1550nm. The a port and the b port of the oscilloscope 6 are both electrical signal input ends. The a port of the avalanche photodetector 7 is an optical signal input port with a wavelength of 1450nm, and the b port is an electrical signal output port. The a port of the sinusoidal signal generator 8 is an input port, and the b port is an output port.

[0041] Specifically, in this embodiment, the sinusoidal signal generator 8 outputs a sinusoidal signal with a frequency of 200 MHz, an amplitude of 100 mV, and a bias of 300 mV. The pulse generator 9 has an output level of 3.3 V ± 1%, a time resolution of 1 ns, and a pulse width range of 1 to (2 32 -1)ns.

[0042] The demodulation principle of the present invention is introduced below.

[0043] The Raman distributed sensing device based on sinusoidal modulated light of the present invention uses the propagation position L in the optical fiber as a reference point to obtain the Raman backscattering signal generated in the sensing optical fiber. The continuous laser emits a stable continuous laser, which enters the optical input end of the electro-optical modulator 2. The electro-optical modulator 2 performs sinusoidal modulation on the continuous laser under the drive of the sinusoidal signal generated by the sinusoidal signal generator 8. The modulated light is amplified and incident on the sensing optical fiber 5. The 1450nm Raman backscattering anti-Stokes scattering signal generated at each point along the sensing optical fiber 5 passes through the wavelength division multiplexer 4, is detected by the photodetector 7 and converted into an electrical signal, and is recorded and stored by the oscilloscope 6. The pulse generator 9 sends out a pulse trigger signal, and triggers the arbitrary signal generator and the oscilloscope at the same time, ensuring that the trigger level can trigger a sinusoidal signal of a certain period. At the same time, the oscilloscope can record the Raman backward anti-Stokes scattering signal generated by the optical signal modulated by the sinusoidal signal in the entire section of optical fiber under the triggering signal. Finally, the oscilloscope is used to perform several cumulative averages to obtain the Raman backward anti-Stokes scattering average signal excited by the optical signal modulated by the triggered sinusoidal signal in the entire section of optical fiber. In this embodiment, the cumulative number of times can be 2000 to 50000 times, specifically, the cumulative number of times is 20000 times. By adjusting the frequency and period number of the modulated sinusoidal signal, the spatial scale corresponding to the entire section of modulated light is greater than the length of the temperature change zone, but the spatial scale corresponding to the single-period modulated optical signal is not greater than the length of the temperature change zone. The position information of the temperature change zone can be demodulated through the "rising zone" of the backward Raman anti-Stokes scattering signal along the optical fiber. The temperature information of the temperature change zone can be obtained by demodulating the specific period signal of the "oscillation zone" signal.

[0044] When the frequency of the sinusoidal signal emitted by the sinusoidal signal generator 8 is 200 MHz, the corresponding period is 5 ns, and the spatial scale corresponding to the single-cycle modulated light is Where c is the speed of light, t is the light propagation time, and n is the refractive index. Here, the single-cycle modulated light corresponds to a spatial scale of l0 = 0.5 m. The pulse generator sends a high-level pulse signal with a duration of 50 ns, which triggers the arbitrary waveform generator to send a 10-cycle sine signal. After accumulating and averaging through the oscilloscope 6, the spontaneous Raman backward anti-Stokes scattering average signal excited by the modulated light transmitted forward in the entire optical fiber and along the line can be obtained. The signal can be expressed as:

[0045]

[0046] in, represents the modulation signal amplitude, ρ as is the Bose-Einstein factor, Γ asis the capture coefficient of the anti-Stokes scattering signal, F is the amplification factor, and α(λ0) and α(λ as ) represent the wavelengths λ0 and λ as The optical power attenuation coefficient, λ0 and λ as are the wavelengths of continuous laser and Raman backscattered anti-Stokes signals, ω m is the modulation angular velocity, t is the modulation time, k m is the group wave number of the modulated light, and L represents the position in the sensing fiber. Among them, there are:

[0047] k m =ω m n gr / c; (2)

[0048]

[0049] n gr is the refractive index of light at different wavelengths, c is the speed of light in a vacuum, h is Planck's constant, Δν is the Raman frequency shift, k is the Boltzmann constant, and T is the temperature of the sensing fiber.

[0050] Specifically, when the length of the temperature change zone is different, the determination of the length of the temperature change zone is divided into the following different situations:

[0051] (1) l0=L0 and N·l0>L0; wherein N represents the number of cycles of the sinusoidal signal output by the sinusoidal signal generator (8) each time, and l0 represents the spatial scale corresponding to a single cycle of modulated light.

[0052] like Figure 2 As shown in the figure, when the spatial scale distance of multi-cycle modulated light (10 cycles) is greater than the length of the temperature change zone, and the spatial scale of single-cycle modulated light is equal to the length of the temperature change zone, the modulated light collected by the oscilloscope is transmitted forward in the entire section of the optical fiber and stimulated along the line. The "rising zone" (Z0~Z1) is the spontaneous Raman backward anti-Stokes scattering signal stimulated from the beginning of the multi-cycle modulated light entering the temperature change zone to the beginning of the first cycle leaving the temperature change zone, and the "oscillation zone" (Z1~Z2) is the spontaneous Raman backward anti-Stokes scattering signal stimulated from the beginning of the first cycle leaving the temperature change zone to the last cycle completely leaving the temperature change zone. Since the "rising zone" and the "oscillation zone" are caused by the temperature change zone, the starting position Z0 of the temperature change zone and the length L0 of the temperature change zone can be determined by locating the rising zone and the oscillation zone, and:

[0053] L0=Z1-Z0; (4)

[0054] Among them, Z1 represents the starting point of the oscillation zone, and Z0 represents the starting point of the rising zone.

[0055] The moment when the first cycle begins to leave the temperature change zone is also the moment when the second cycle begins to enter the temperature change zone. At this time, since l0=L0, Z1 also corresponds to the moment when the first cycle completely enters the temperature change zone; therefore, the "oscillation zone" is also equivalent to the spontaneous Raman back anti-Stokes scattering signal excited by the process from the second cycle of the multi-cycle modulated light entering the temperature change zone to the multi-cycle modulated light leaving the temperature change zone. Since the multi-cycle modulated light has periodicity, the "oscillation zone" also has periodicity. By analyzing the autocorrelation coefficient of the "oscillation zone" curve, the periodicity contained therein can be found, and the period can be calculated by the correlation coefficient. For the discrete signal x[n] corresponding to the spontaneous Raman back anti-Stokes scattering signal, its R xx [m] The calculation formula of the autocorrelation coefficient is:

[0056]

[0057] Where m is the delay, which represents the offset of the signal compared to itself. x[n] and x[n+m] represent the nth and n+mth data points of the original signal, respectively. When the signal is periodic, its autocorrelation function will also be periodic, and the period is the same as the original signal. In addition, when the delay is equal to the signal period or an integer multiple thereof, a peak value will appear in the autocorrelation function. Therefore, by performing autocorrelation calculation on the spontaneous Raman backward anti-Stokes scattering signal, the oscillation period of the scattering curve can be determined, thereby determining each modulation period of the stimulated spontaneous Raman backward anti-Stokes scattering signal. Then, according to the period obtained by the autocorrelation calculation, the spontaneous Raman backward anti-Stokes scattering periodic signal of any period in the "oscillation zone" can be extracted. The signal can be regarded as a spontaneous Raman backward anti-Stokes scattering signal stimulated by an equivalent pulse signal, and then a single-channel demodulation is performed to obtain the temperature of the temperature change zone. In this embodiment, the signal of the last period of the "oscillation zone" stage is uniformly used to demodulate the temperature of the temperature change zone.

[0058] During temperature demodulation, the calibration phase is first performed. The temperature of the calibration fiber ring is set to be constant at T0. The Raman backscattering anti-Stokes signal intensity in the calibration fiber ring is measured by an avalanche detector. Then, after obtaining the period of the scattering signal through autocorrelation, the spontaneous Raman backscattering anti-Stokes signal intensity φ of a certain period in the "oscillation zone" stage is intercepted. a0 (T, L); in the measurement phase, the Raman backward anti-Stokes light signal intensity in the sensing fiber is measured by the avalanche detector, and then the spontaneous Raman backward anti-Stokes scattering signal intensity φ corresponding to the period in the "oscillation zone" phase is intercepted after obtaining the period of the scattering signal through autocorrelation a(T, L); Finally, the calculation stage is carried out. According to the previous calibration steps and measurement steps, the temperature information of the temperature change zone is calculated, and the measurement result is obtained. The calculation formula is:

[0059]

[0060] Where T0 is the temperature at calibration, h is Planck's constant, Δν is the Raman frequency shift, and k is the Boltzmann constant. The temperature information of the temperature change zone can be demodulated.

[0061] (2) l0<L0 and N·l0>L0; wherein N represents the number of cycles of the sinusoidal signal output by the sinusoidal signal generator (8) each time, and l0 represents the spatial scale corresponding to a single cycle of the modulated light.

[0062] like Figure 3 As shown in the figure, when the spatial scale distance of multi-cycle modulated light (10 cycles) is greater than the length of the temperature variation zone, and the spatial scale of single-cycle modulated light is less than the length of the temperature variation zone, the "rising zone" (Z0~Z1) represents the spontaneous Raman backward anti-Stokes scattering signal excited from the beginning of the multi-cycle modulated light entering the temperature variation zone to the beginning of the first cycle of the modulated light leaving the temperature variation zone, and the "oscillation zone" (Z1~Z2) represents the spontaneous Raman backward anti-Stokes scattering signal excited from the beginning of the first cycle of the modulated light leaving the temperature variation zone until the last cycle leaves the temperature variation zone. Similarly, since the multi-cycle modulated light is periodic, the subsequent "oscillation zone" (Z1~Z2) is also periodic. At this time, the starting position of the temperature variation zone is Z0, and the length of the temperature variation zone L0 is:

[0063] L0=Z1-Z0; (7)

[0064] The moment when the first cycle completely enters the temperature change zone is also the moment when the second cycle begins to enter the temperature change zone. Since l0<L0, in this case, the moment when the first cycle begins to leave the temperature change zone is greater than the moment when the first cycle begins to completely enter the temperature change zone; at this time, although the signal peak position is different, the length of the temperature change zone can still be demodulated by the moment when the first cycle begins to leave the temperature change zone; in addition, the temperature in the temperature change zone is still demodulated in a single channel through the spontaneous Raman backward anti-Stokes scattering signal of the last cycle in the "oscillation zone" stage.

[0065] (3) When l0>L0, it is necessary to increase the frequency of the modulation signal, thereby reducing the spatial scale l0 of the single-cycle modulated light until the spatial scale of the single-cycle modulated light is less than or equal to the length of the temperature change zone, and then use the above method for demodulation.

[0066] If conditions permit, the spatial resolution of the system can be improved by increasing the frequency of the modulated light as much as possible. For example, when the frequency of the sinusoidal signal of the modulated light is 1 GHz, its single period is 1 ns, which corresponds to a spatial scale of 0.1 m. In theory, it can measure temperature change zones with a distance greater than or equal to 0.1 m. That is, if conditions permit, the greater the frequency of the modulated signal, the better the corresponding spatial resolution of the system.

[0067] Embodiment 2

[0068] Embodiment 2 of the present invention provides a Raman distributed sensing method based on sinusoidal modulated light. Figure 1 The device shown is implemented, comprising the following steps:

[0069] Step 1: Control the sinusoidal signal generator 8 to output a sinusoidal signal of N cycles, and receive the Raman backscattered anti-Stokes signal output from the sensing optical fiber 5 through the oscilloscope 6; wherein the value of N is 5 to 100; in this embodiment, the value of N is 10.

[0070] The step 1 also includes the following steps: adjusting the period of the sinusoidal signal output by the sinusoidal signal generator 8 so that the corresponding spatial scale l0 satisfies the following conditions: l0≤L0 and N·l0>L0; wherein L0 represents the length of the temperature change zone.

[0071] Step 2: Repeat step 1, use an oscilloscope to obtain the Raman backscattering anti-Stokes signal multiple times and perform cumulative averaging to obtain the Raman backscattering anti-Stokes average signal excited in the entire sensing optical fiber (5);

[0072] Step 3: Determine the starting position and length of the temperature change zone according to the positions of the rising zone and the oscillation zone in the temperature change zone in the average signal of the Raman backscattering anti-Stokes scattering excited in the entire sensing optical fiber (5).

[0073] In step 3, the calculation formula for the length of the temperature change zone is the above formula (4) or (7).

[0074] Step 4: Calculate the temperature information of the temperature change zone according to the signal intensity of any period of the oscillation zone of the Raman backscattering anti-Stokes average signal. In step 4, the temperature information of the temperature change zone is calculated by the above formula (6).

[0075] Specifically, the step 4 also includes the step of performing autocorrelation operation on the Raman backscattering anti-Stokes average signal excited in the entire sensing optical fiber 5 to obtain an autocorrelation coefficient, and then extracting the spontaneous Raman backscattering anti-Stokes average signal excited by the single-cycle modulation signal according to the periodicity of the autocorrelation coefficient. Specifically, in this embodiment, the spontaneous Raman backscattering anti-Stokes average signal of the last cycle is extracted for temperature demodulation in the temperature variation zone.

[0076] 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 sensing device based on sinusoidal modulated light, characterized in that: include: A continuous laser (1), an electro-optic modulator (2), an optical amplifier (3), a wavelength division multiplexer (4), a sensing optical fiber (5), a photodetector (7), a sinusoidal signal generator (8), and an oscilloscope (6); the electro-optic modulator (2) is used to perform sinusoidal modulation on the continuous laser output by the continuous laser (1) under the drive of the sinusoidal signal output by the sinusoidal signal generator (8); the modulated laser light is amplified by the optical amplifier (3) and then incident on the sensing optical fiber (5) through the wavelength division multiplexer (4); the Raman backward anti-Stokes scattering signal generated at each point in the sensing optical fiber is output by the wavelength division multiplexer (4) and then detected by the photodetector (7); the detection signal output by the photodetector (7) is received and recorded by the oscilloscope (6) and then sent to a calculation unit to calculate and obtain the position information and temperature information of the temperature change zone.

2. The Raman distributed sensing device based on sinusoidal modulated light according to claim 1, characterized in that: The continuous laser (1) is a semiconductor laser, the optical amplifier (3) is an erbium-doped fiber amplifier, the sinusoidal signal generator (8) is an arbitrary waveform generator, the photodetector (7) is an avalanche photodetector, and the frequency of the sinusoidal signal output by the sinusoidal signal generator (8) is 100 MHz to 10 GHz.

3. The Raman distributed sensing device based on sinusoidal modulated light according to claim 1, characterized in that: It also comprises a pulse generator (9), the output end of which is connected to the sine signal generator (8) and the oscilloscope (6) and is used to output a pulse trigger signal to simultaneously trigger the sine signal generator (8) and the oscilloscope (6).

4. The Raman distributed sensing device based on sinusoidal modulated light according to claim 1, characterized in that: The wavelength of the continuous laser (1) is centered at 1550 nm, and the wavelength of the Raman backscattered anti-Stokes signal is 1450 nm; the wavelength of the port of the wavelength division multiplexer (4) connected to the optical amplifier (3) is 1550 nm, the wavelength of the port connected to the sensing optical fiber (5) is 1550 nm & 1450 nm, and the wavelength of the port connected to the photodetector (7) is 1450 nm.

5. A Raman distributed sensing method based on sinusoidal modulated light, characterized in that: The device according to any one of claims 1 to 4 is implemented, comprising the following steps: Step 1: Control the sinusoidal signal generator (8) to output a sinusoidal signal of N cycles, and receive the Raman backscattered anti-Stokes signal output from the sensing optical fiber (5) through an oscilloscope (6); wherein the value of N is 5 to 100; Step 2: Repeat step 1, use an oscilloscope to obtain the Raman backscattering anti-Stokes signal multiple times and perform cumulative averaging to obtain the Raman backscattering anti-Stokes average signal excited in the entire sensing optical fiber (5); Step 3: Determine the starting position and length of the temperature change zone according to the positions of the rising zone and the oscillation zone in the temperature change zone in the average signal of the Raman backscattering anti-Stokes scattering excited in the entire sensing optical fiber (5); Step 4: Calculate the temperature information of the temperature change zone according to the signal intensity of any period in the oscillation zone of the Raman backscattering anti-Stokes average signal.

6. The Raman distributed sensing method based on sinusoidal modulated light according to claim 5, characterized in that: In step 3, the temperature information calculation formula of the temperature change zone is: Where T represents the temperature in the temperature change zone, φ a (T,L) and φ a0 (T, L) are the spontaneous Raman backscattering anti-Stokes scattering signal intensities of the same period in the "oscillation zone" stage measured during measurement and calibration, T0 is the temperature during calibration, h is Planck's constant, Δν is the Raman frequency shift, and k is the Boltzmann constant.

7. The Raman distributed sensing method based on sinusoidal modulated light according to claim 6, characterized in that: The step 4 also includes the step of performing autocorrelation operation on the average signal of Raman backward anti-Stokes scattering excited in the entire section of the sensing optical fiber (5) to obtain an autocorrelation coefficient, and then extracting the average signal of spontaneous Raman backward anti-Stokes scattering excited by the single-cycle modulation signal according to the periodicity of the autocorrelation coefficient.

8. The Raman distributed sensing method based on sinusoidal modulated light according to claim 7, characterized in that: The calculation formula of the autocorrelation coefficient is: Where x[n] and x[n+m] represent the nth and n+mth data points of the original signal, respectively, m represents the delay, R xx [m] represents the autocorrelation coefficient.

9. The Raman distributed sensing method based on sinusoidal modulated light according to claim 5, characterized in that: In step 3, the calculation formula for the length of the temperature change zone is: L0=Z1-Z0; Among them, L0 represents the length of the temperature change zone, Z1 represents the starting point of the oscillation zone, and Z0 represents the starting point of the rising zone.

10. The Raman distributed sensing method based on sinusoidal modulated light according to claim 5, characterized in that: The step 1 further includes the following steps: adjusting the period of the sinusoidal signal output by the sinusoidal signal generator (8) so that the corresponding spatial scale l0 satisfies the following conditions: l0≤L0 and N·l0>L0; wherein L0 represents the length of the temperature change zone.

Images