A submarine cable acoustic monitoring system based on scattering fiber fingerprint technology

Abstract

This invention discloses a submarine cable acoustic monitoring system based on scattering-type fiber optic fingerprint technology, belonging to the field of fiber optic sensing technology. The system includes a light source module, a transmitting module, a submarine cable fiber optic sensing unit, a dual-balanced detector module, and a signal processing module. In the light source module, the continuous light output from the laser is split into a probe light and a local reference light by a dynamic beam splitter. The probe light is modulated and injected into the submarine cable fiber, and the resulting backscattered Rayleigh light carries acoustic information back. The dual-balanced detector module has a built-in light intensity monitoring unit that monitors the light intensity of the reference light and the scattered light in real time. By comparing the two intensities, it sends a feedback control signal to the dynamic beam splitter, dynamically adjusting the splitting ratio to maximize the interference term intensity coefficient, thereby improving the signal amplitude and sensing sensitivity. This invention solves the problems of limited sensing distance and high laser linewidth requirements in traditional systems, and is suitable for long-distance, high-reliability submarine cable acoustic event monitoring and location in deep-sea environments.

Description

Technical Field

[0001] This invention relates to the field of fiber optic sensing technology, and more specifically to a submarine cable acoustic monitoring system based on scattering fiber optic fingerprint technology. Background Technology

[0002] In marine engineering, submarine cables serve as critical infrastructure for global communication and energy transmission. They are susceptible to interference from the external environment and human activities, such as ship anchoring, earthquakes, fishing activities, or human sabotage, leading to signal interruptions or physical damage. Once a submarine cable fails, it not only incurs high repair and emergency maintenance costs but also triggers a chain reaction of communication and energy transmission disruptions, causing significant economic losses and social impacts. Therefore, developing acoustic monitoring technologies for submarine cables with high precision and long-distance monitoring capabilities is of paramount importance for ensuring the safe and stable operation of submarine cables throughout their entire lifecycle.

[0003] A significant portion of currently laid submarine cables are fiber optic composite cables. These cables combine the dual functions of power transmission and fiber optic communication. Their built-in communication fibers provide the hardware foundation for optical sensing technology applications and open up an effective path to solving the challenges of submarine cable monitoring. Phase-sensitive optical time-domain reflectometry (φ-OTDR) technology, as a mainstream technology in the field of fiber optic sensing, uses narrow-linewidth lasers to emit light pulses and sense external vibrations by detecting and demodulating interference traces generated by Rayleigh scattering in the fiber. It possesses the inherent advantages of non-invasive and distributed monitoring. However, when applied to actual submarine cable monitoring scenarios, this technology still faces two major technical bottlenecks, making it difficult to meet actual engineering needs.

[0004] First, it places stringent requirements on laser linewidth and suffers from insufficient stability. Traditional φ-OTDR technology heavily relies on narrow-linewidth lasers to ensure the clarity of interference traces within the optical pulse, enabling accurate identification of vibration signals. When environmental or cost constraints lead to insufficient laser linewidth, phase noise within the pulse increases, interference traces become blurred, and the sensitivity to external vibrations drops sharply. Furthermore, lasers are susceptible to temperature fluctuations and mechanical vibrations, making linewidth stability difficult to guarantee. This results in a high false alarm rate and poor reliability in the monitoring system, causing it to fail during long-distance monitoring.

[0005] Secondly, the signal demodulation method is limited, restricting the sensing distance. Traditional systems use direct demodulation, relying solely on the intensity information of backscattered Rayleigh light and the photodetector receiving the scattered light signal. Since Rayleigh scattered light power is very weak and attenuates with increasing fiber optic transmission distance, signal gain is difficult to improve. To maintain a detectable signal-to-noise ratio, the effective sensing distance of the system is usually limited. In long-distance submarine cable monitoring, repeaters are required, which not only increases the construction and maintenance costs of the system but also introduces additional fault points, making continuous and uninterrupted monitoring of the entire submarine cable impossible.

[0006] Therefore, developing a long-distance, high-precision, all-weather acoustic monitoring system for submarine cables to overcome the application bottlenecks of traditional φ-OTDR technology has become a key technical problem that urgently needs to be solved in the field of marine engineering. Summary of the Invention

[0007] The purpose of this invention is to provide a submarine cable acoustic monitoring system based on scattering fiber fingerprint technology. The system uses a portion of the continuous light output from the light source as the local reference light and performs balanced detection with the backscattered Rayleigh light. By monitoring the intensity of the two light sources in real time and dynamically adjusting the splitting ratio, the system maximizes the interference gain under the condition of a certain light source power, significantly improving the sensitivity and resolution of vibration sensing and extending the monitoring distance. At the same time, it solves the problems of high laser linewidth requirements and low signal gain of traditional φ-OTDR.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is: a submarine cable acoustic monitoring system based on scattering fiber optic fingerprint technology, comprising: The light source module includes a laser and a dynamic beam splitter. The laser is used to generate continuous laser light, and the dynamic beam splitter is used to split the continuous laser light into a probe light and a local reference light, and can dynamically adjust the intensity ratio of the probe light and the local reference light according to the received feedback control signal. The transmitting module is used to modulate the probe light into an optical pulse and inject it into the submarine cable fiber optic sensing unit, and to guide the backscattered Rayleigh light generated by the submarine cable fiber optic sensing unit back to the dual-balanced detector module. The submarine cable fiber optic sensing unit uses the fiber optic cable itself as the sensing medium to generate backscattered Rayleigh light carrying acoustic information under the action of external acoustic vibration. The dual-balance detector module includes a light intensity monitoring unit, an optical mixer, and a photoelectric conversion unit. The light intensity monitoring unit monitors the light intensity of the local reference light and the backscattered Rayleigh light in real time, and sends a feedback control signal to the dynamic beam splitter based on the comparison of their light intensities to adjust the beam splitting ratio to achieve optimal monitoring results. The optical mixer mixes the adjusted local reference light and the backscattered Rayleigh light and outputs an interference light signal. The photoelectric conversion unit converts the interference light signal into an electrical signal carrying acoustic information. The signal processing module is used to acquire and process the electrical signal, extract acoustic information, and identify the type and location of acoustic events.

[0009] Furthermore, the dynamic beam splitter divides the continuous light output by the laser into a probe beam and a local reference beam according to a preset initial ratio. The preset initial ratio is that the light with 90% energy is used as the probe beam and the light with 10% energy is used as the local reference beam.

[0010] The beneficial effects are as follows: by setting a preset initial ratio, the system has a reasonable energy distribution basis in the startup phase, which not only ensures sufficient detection optical power to achieve long-distance transmission, but also provides local reference light for coherent detection, laying a good initial state for subsequent dynamic feedback control and ensuring that the system can still work normally before entering stable feedback adjustment.

[0011] Furthermore, the optical mixer performs frequency mixing processing on the local reference light and the backscattered Rayleigh light, specifically as follows: Let the local reference photoelectric field intensity be in, For reference optical amplitude, As a reference light angular frequency, The initial phase of the reference light; Suppose there is an external acoustic disturbance signal at the incident end x of the distance probe light in the optical fiber, and the electric field strength of the backscattered Rayleigh light transmitted to the input of the optical mixer is: in, Let x be the amplitude of the scattered light at the incident end of the probe light. To detect the angular frequency of light, This is the time delay for the backscattered Rayleigh light to travel to the mixer input. This refers to the dynamic phase change caused by external disturbances. The inherent scattering phase at the incident end of the probe light x is determined by the microstructure of the optical fiber and does not change with time. The total light intensity after the local reference light and the backscattered Rayleigh light are coupled by the optical mixer is: in, The intensity of the local reference light, The intensity of the backscattered Rayleigh light; The total phase difference is expressed as: because , , All of these are constants that do not change with time, and their sum is considered as a fixed bias phase. Therefore, the total phase difference simplifies to: Substituting into the total light intensity formula, the interference term light intensity is: The intensity of the interference term will affect the dynamic phase change caused by external acoustic disturbances. This is converted into periodic fluctuations in light intensity, enabling the extraction of acoustic information.

[0012] The beneficial effects are as follows: by clarifying the physical mapping relationship between the light intensity of the interference term and the dynamic phase change, the system can transform the small phase change caused by external acoustic disturbance into a detectable periodic fluctuation of light intensity, providing a solid theoretical basis for the extraction of phase information.

[0013] Furthermore, the adjustment of the beam splitting ratio to achieve optimal monitoring effect means that the interference term intensity coefficient reaches its maximum value. Specifically, this is achieved through real-time monitoring by the intensity monitoring unit and feedback control by the dynamic beam splitter, ensuring that the intensity of the local reference light is... Light intensity of backscattered Rayleigh light They satisfy the equality relationship, where x is the distance between the position on the optical fiber affected by the external acoustic disturbance and the incident end of the probe light.

[0014] The beneficial effects are: this limitation provides a clear target orientation for feedback control, giving the monitoring of the light intensity monitoring unit and the adjustment of the dynamic beam splitter a clear physical basis, ensuring that the system can work stably at the optimal signal-to-noise ratio.

[0015] Furthermore, the light intensity adjustment amount corresponding to the feedback control signal sent by the light intensity monitoring unit to the dynamic beam splitter is determined by the following formula: In the formula, The light intensity of the local reference light initially measured by the light intensity monitoring unit. The intensity of the backscattered Rayleigh light initially measured by the light intensity monitoring unit; This is the light intensity adjustment amount; if Then adjust the dynamic beam splitter to reduce the local reference beam. Then adjust the dynamic beam splitter to increase the local reference beam.

[0016] The beneficial effects are: ensuring that the adjustment process quickly converges to the optimal state of equal light intensity, significantly improving the system's response speed and control accuracy.

[0017] Furthermore, the submarine cable fiber optic sensing unit uses the existing optoelectronic composite fiber optic cable in the submarine cable as the sensing medium to achieve non-invasive monitoring of the submarine cable.

[0018] The benefits are: no need to lay additional dedicated sensing optical fibers, which greatly reduces the difficulty and cost of construction, and avoids secondary damage to submarine cables that may be caused by laying construction, thus having good economic and engineering practicality.

[0019] Furthermore, the photoelectric conversion unit includes an InGaAs photodetector unit and a transimpedance amplifier, used to convert optical signals into voltage signals.

[0020] The beneficial effects are as follows: by using an InGaAs photodetector unit in conjunction with a transimpedance amplifier, weak interference light signals can be efficiently converted into voltage signals, while also possessing low noise and high gain characteristics, providing high-quality raw data for subsequent signal processing.

[0021] Furthermore, the signal processing module includes: An analog-to-digital conversion unit is used to perform high-precision sampling and digital conversion of the electrical signal; The digital signal processing unit has a built-in phase demodulation algorithm, which is used to demodulate, filter and transform the digitized signal to extract phase information; The acoustic analysis unit has a built-in acoustic event feature library and evaluation model, which is used to identify the type, intensity, and location of acoustic events and assess the hazard level based on the extracted phase information. The feature library includes signal feature templates for ship noise, fishery operation vibration, anchor impact, and seismic waves.

[0022] Furthermore, the laser is a semiconductor laser with a linewidth ≤ 10 kHz and an output light wavelength range of 1550 nm.

[0023] Furthermore, the transmitting module includes a pulse electro-optic modulator and a circulator; the modulation frequency range of the pulse electro-optic modulator is 1kHz~1MHz, and the output optical pulse width adjustment range is 10ns~100ns.

[0024] The beneficial effects of the above scheme are as follows: 1. This system significantly improves detection sensitivity, monitoring distance, positioning accuracy, and frequency response range. Through closed-loop feedback control consisting of a light intensity monitoring unit and a dynamic beam splitter, the local reference light and the backscattered Rayleigh light are matched in real time, maximizing interference gain. This enables the system to detect extremely weak acoustic disturbances (such as distant anchor strikes and undersea earthquakes), extending the effective monitoring distance to over 60 kilometers, achieving a positioning accuracy better than 50 meters, and expanding the frequency response range to 100Hz~60kHz, providing a high-quality data foundation for the accurate identification and hazard assessment of acoustic events.

[0025] 2. This invention optimizes the utilization of light source energy, maximizing signal output under limited power while suppressing fiber nonlinear effects. With a fixed total laser power, dynamic beam splitting optimization ensures that all energy is used to enhance the amplitude of the interference signal, avoiding energy waste caused by improper beam splitting ratios. Since it eliminates the need to compensate for insufficient gain by simply increasing the probe light power, the risk of nonlinear effects in the fiber is effectively suppressed, thus ensuring the long-term stable operation of the system.

[0026] 3. The system boasts strong environmental adaptability, enabling reliable all-weather, unattended monitoring. It can track signal intensity fluctuations caused by factors such as temperature changes, mechanical stress, and localized losses in the marine environment in real time, and automatically correct the beam splitting ratio to ensure the system always operates in optimal condition. This closed-loop adaptive capability eliminates the need for manual intervention and periodic calibration, giving the system extremely high environmental adaptability and long-term reliability, truly achieving all-weather, unattended monitoring of submarine cables.

[0027] 4. This invention is highly economical and practical, facilitating widespread application. By improving the coherent detection gain, the stringent requirements on laser linewidth are relaxed, allowing for the use of lower-cost and more stable lasers while still meeting performance requirements, thus reducing system costs and sensitivity to ambient temperature. Simultaneously, the system employs non-invasive monitoring, significantly simplifying the construction process and reducing construction and maintenance costs, laying a solid foundation for the large-scale engineering application of submarine cable safety monitoring. Attached Figure Description

[0028] Figure 1 This is a system structure diagram of the present invention; Figure 2 This is a flowchart of the measurement process of the present invention.

[0029] The diagram is labeled as follows: 1. Light source module; 2. Laser; 3. Dynamic beam splitter; 4. Transmitter module; 5. Pulse electro-optic modulator; 6. Circulator; 7. Submarine cable fiber optic sensing unit; 8. Dual-balanced detector module; 9. Light intensity detection unit; 10. Optical mixer; 11. Photoelectric conversion unit; 12. Signal processing module; 13. Analog-to-digital conversion unit; 14. Digital signal processing unit; 15. Acoustic analysis unit. Detailed Implementation

[0030] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0031] It should be noted that, unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0032] Example 1 like Figure 1 As shown, this embodiment provides a submarine cable acoustic monitoring system based on scattering fiber fingerprint technology, including a light source module 1, a transmitting module 4, a submarine cable fiber optic sensing unit 7, a dual-balanced detector module 8, and a signal processing module 12.

[0033] The light source module 1 includes a laser 2 and a dynamic beam splitter 3. The laser 2 is a semiconductor laser with a linewidth ≤10kHz, outputting continuous laser light in the 1550nm wavelength band. The input of the dynamic beam splitter 3 is connected to the output of the laser 2, splitting the received continuous laser light into two paths: one path is output as probe light to the transmitting module 4, and the other path is output as local reference light to the dual-balanced detector module 8. The dynamic beam splitter 3 also has a feedback control signal input, used to receive feedback control signals from the dual-balanced detector module 8 and dynamically adjust the intensity ratio of the probe light to the local reference light according to these signals.

[0034] The transmitting module 4 includes a pulsed electro-optic modulator 5 and a circulator 6. The input of the pulsed electro-optic modulator 5 is connected to the probe light output of the dynamic beam splitter 3, with a modulation frequency range of 1 kHz to 1 MHz and an output light pulse width adjustment range of 10 ns to 100 ns. The output of the pulsed electro-optic modulator 5 is connected to the first port P1 of the circulator 6, used to inject the modulated light pulse into the circulator 6. The second port P2 of the circulator 6 is connected to the submarine cable fiber optic sensing unit 7, used to inject the light pulse into the sensing fiber and receive the backscattered Rayleigh light generated by the sensing fiber. The third port P3 of the circulator 6 is connected to the dual-balanced detector module 8, used to guide the backscattered Rayleigh light to the dual-balanced detector module 8.

[0035] The submarine cable fiber optic sensing unit 7 uses the existing optical fiber in the submarine cable as the sensing medium, eliminating the need for additional dedicated sensing fiber. When external acoustic vibrations act on the submarine cable, the refractive index of the fiber changes, causing phase modulation of the light pulses transmitted within it, thereby forming backscattered Rayleigh light carrying acoustic information.

[0036] The dual-balance detector module 8 includes a light intensity monitoring unit 9, an optical mixer 10, and a photoelectric conversion unit 11. The light intensity monitoring unit 9 has a first input terminal IN1 and a second input terminal IN2, wherein the first input terminal IN1 is connected to the local reference light output terminal of the dynamic beam splitter 3, and the second input terminal IN2 is connected to the third port P3 of the circulator 6. The light intensity monitoring unit 9 is used to monitor the light intensity of the local reference light and the backscattered Rayleigh light in real time, and generate a feedback control signal based on the comparison result between the two. This signal is sent to the feedback control signal input terminal of the dynamic beam splitter 3 via the feedback control signal output terminal. The light intensity monitoring unit 9 also has a first output terminal OUT1 and a second output terminal OUT2, which are directly connected to the first input terminal IN1 and the second input terminal IN2, respectively, for transmitting the local reference light and the backscattered Rayleigh light to the subsequent optical mixer 10.

[0037] The two input terminals of the optical mixer 10 are connected to the first output terminal OUT1 and the second output terminal OUT2 of the light intensity monitoring unit 9, respectively, for mixing the local reference light after adjusting the light intensity with the backscattered Rayleigh light to output an interference light signal. The input terminal of the photoelectric conversion unit 11 is connected to the output terminal of the optical mixer 10. It includes an InGaAs photodetector unit and a transimpedance amplifier, for converting the interference light signal into an electrical signal carrying acoustic information. The InGaAs photodetector unit uses an InGaAs phototube.

[0038] The signal processing module 12 includes an analog-to-digital converter (ADC) 13, a digital signal processing unit (DSC) 14, and an acoustic analysis unit 15. The input of the ADC 13 is connected to the output of the photoelectric conversion unit 11, used for high-precision sampling and digitization of electrical signals. The input of the DSC 14 is connected to the output of the ADC 13, and it has a built-in phase demodulation algorithm for demodulating, filtering, and transforming the digitized signal to extract the phase signal containing acoustic information. The input of the acoustic analysis unit 15 is connected to the output of the DSC 14, and it has a built-in acoustic event feature library and evaluation model. The feature library contains pre-stored signal feature templates for typical acoustic events such as ship noise, vibrations from fishing operations, anchor impacts, and seismic waves. Based on the extracted phase information, the acoustic analysis unit 15 identifies the type, intensity, and location of the acoustic event through feature matching and threshold comparison, and assesses the hazard level.

[0039] Example 2 like Figure 2 As shown, this embodiment details the system's workflow, particularly the specific process of maximizing the interference term light intensity coefficient through feedback control of the light intensity monitoring unit and the dynamic beam splitter.

[0040] Step 1: After the system starts, laser 2 outputs continuous laser light, and dynamic beam splitter 3 splits the continuous light into probe light and local reference light according to a preset initial ratio. In this embodiment, the preset initial ratio is 9:1. 90% energy light is connected to the emission module as probe light through optical path a, and 10% energy light is connected to the first input terminal IN1 of the light intensity monitoring unit 9 of the dual-balanced detector module 8 as local reference light through optical path b.

[0041] Step 2: The probe light is modulated into an optical pulse by the pulse electro-optic modulator 5 and injected into the submarine cable optical fiber sensing unit 7 through the circulator 6. The optical pulse propagates in the sensing fiber and is modulated by external acoustic vibrations to generate backscattered Rayleigh light. This scattered light is returned to the dual-balanced detector module 8 through the circulator 6 and connected to the second input terminal IN2 of the light intensity monitoring unit 9 through the third port P3.

[0042] Step 3: The light intensity monitoring unit 9 monitors the light intensity of the local reference light at the first input terminal IN1 and the light intensity of the backscattered Rayleigh light at the second input terminal IN2 in real time, and calculates the light intensity adjustment amount fed back to the dynamic beam splitter 3 based on the measured light intensity signal. At the same time, the local reference light and the backscattered Rayleigh light are input to the optical mixer 10 for coupling, and the coupled interference light signal is output.

[0043] Let the local reference photoelectric field intensity be: in, For reference optical amplitude, As a reference light angular frequency, The initial phase of the reference light.

[0044] Suppose there is an external acoustic disturbance signal at the incident end x of the distance probe light in the optical fiber, and the electric field strength of the backscattered Rayleigh light transmitted to the input of the optical mixer is: in, Let x be the amplitude of the scattered light at the incident end of the probe light. To detect the angular frequency of light, This is the time delay for the backscattered Rayleigh light to travel to the mixer input. This refers to the dynamic phase change caused by external disturbances. The inherent scattering phase at the incident end of the probe light x is determined by the microstructure of the optical fiber and does not change with time. The total light intensity after the local reference light and the backscattered Rayleigh light are coupled by the optical mixer is: in, The intensity of the local reference light, The intensity of the backscattered Rayleigh light; , , The total phase difference is expressed as: because , , All of these are constants that do not change with time, and their sum is considered as a fixed bias phase. Therefore, the total phase difference simplifies to: Substituting into the total light intensity formula, the interference term light intensity is: The intensity of the interference term will affect the dynamic phase change caused by external acoustic disturbances. This is converted into periodic fluctuations in light intensity, enabling the extraction of acoustic information.

[0045] When there is no external disturbance The interference light intensity is a fixed value; when there is an external disturbance, As time changes, the intensity of the interference light will fluctuate periodically, realizing the conversion of phase information into light intensity information. Furthermore, due to the introduction of high-power local reference light, the signal amplitude is also amplified synchronously, thereby significantly improving the signal strength after photoelectric conversion and introducing additional frequency conversion gain to the signal, effectively extending the sensing distance.

[0046] To obtain the maximum amplitude of the interference term intensity, the intensity coefficient of the interference term must be required. When the maximum value is reached, assuming there is an acoustic disturbance signal at point x, the incident end of the probe light in the fiber optic cable, the attenuation of the probe light is determined solely by x. Since the total intensity of the laser is constant, the intensity of the reference light... Light intensity of backscattered Rayleigh light The sum is a constant, and thus we can obtain the current value. and When they are equal, the light intensity coefficient of the interference term reaches its maximum value.

[0047] The light intensity of the reference light was initially measured by the light intensity monitoring unit. Light intensity of backscattered Rayleigh light Then, the light intensity monitoring unit 9 sends a feedback control signal to the dynamic beam splitter 3. The dynamic beam splitter 3 adjusts the beam splitting ratio according to the feedback signal. Let the adjustment amount of the dynamic beam splitter 3 to the light intensity be... Therefore, in order to maximize the intensity coefficient of the interference term, the adjustment amount of the dynamic beam splitter 3 to the light intensity should be: In the formula, The light intensity of the local reference light initially measured by the light intensity monitoring unit. The intensity of the backscattered Rayleigh light initially measured by the light intensity monitoring unit; This is the light intensity adjustment amount; if Then adjust the dynamic beam splitter to reduce the local reference beam. Then adjust the dynamic beam splitter to increase the local reference beam.

[0048] Step 4: The local reference light and the backscattered Rayleigh light from the initial beam splitting are coupled and interfered by the optical mixer 10 to the photoelectric conversion unit 11, which converts the optical signal into an electrical signal.

[0049] Step 5: The analog-to-digital conversion unit 13 performs high-precision sampling and digital conversion on the electrical signal output by the dual-balanced detection module 8, with a high sampling rate and wide dynamic range, to ensure the complete acquisition of weak differential electrical signals.

[0050] Step 6: The digital signal processing unit 14 performs phase demodulation, noise filtering and signal transformation processing on the digitized signal. It has a built-in phase demodulation algorithm, which, combined with phase unwrapping technology, obtains the location of the anomaly.

[0051] Step 7: The acoustic analysis unit 15 maps the processed signal data into specific acoustic events and completes event type identification, noise intensity quantification, and hazard level assessment.

[0052] Step 8: Adjust the light intensity based on the dynamic beam splitter 3 calculated in Step 3. The dynamic beam splitter 3 adjusts the beam splitting according to the feedback control signal. The local reference light and the backscattered Rayleigh light are coupled and interfered by the optical mixer 10 to the photoelectric conversion unit 11, which converts the optical signal into an electrical signal.

[0053] Step 9: Repeat steps 5 to 7 to obtain the precision measurement results.

[0054] The system performance was tested and verified using the aforementioned system structure and control method. Under typical operating conditions, the laser 2 output power was 100mW, the pulse width of the pulse electro-optic modulator 5 was set to 100ns, and the pulse repetition frequency was matched with the length of the sensing fiber. Test results show that the effective monitoring distance of this system can reach over 60 kilometers, the acoustic vibration frequency measurement range is 100Hz to 60kHz, and the event positioning accuracy is better than 50 meters.

[0055] In real-world submarine cable monitoring scenarios, this system can effectively detect acoustic events such as ship anchoring and unanchoring, seismic wave propagation, and interference from fishing activities. Thanks to the adoption of adaptive light intensity modulation and coherent detection technology, the system maintains a high signal-to-noise ratio and sensitivity even at long-distance monitoring terminals, ensuring the reliability and accuracy of monitoring.

[0056] Finally, it should be noted that any parts of this invention not described in detail are prior art. Those skilled in the art will understand that the above descriptions are merely preferred embodiments of the invention and are not intended to limit the invention. Although the invention has been described in detail with reference to the foregoing examples, those skilled in the art can still modify the technical solutions described in the foregoing examples or make equivalent substitutions for some of the technical features. All modifications and equivalent substitutions made within the spirit and principles of the invention should be included within the scope of protection of the invention.

Claims

1. A submarine cable acoustic monitoring system based on scattering fiber optic fingerprint technology, characterized in that, include: The light source module includes a laser and a dynamic beam splitter. The laser is used to generate continuous laser light, and the dynamic beam splitter is used to split the continuous laser light into a probe light and a local reference light, and can dynamically adjust the intensity ratio of the probe light and the local reference light according to the received feedback control signal. The transmitting module is used to modulate the probe light into an optical pulse and inject it into the submarine cable fiber optic sensing unit, and to guide the backscattered Rayleigh light generated by the submarine cable fiber optic sensing unit back to the dual-balanced detector module. The submarine cable fiber optic sensing unit uses the fiber optic cable itself as the sensing medium to generate backscattered Rayleigh light carrying acoustic information under the action of external acoustic vibration. The dual-balance detector module includes a light intensity monitoring unit, an optical mixer, and a photoelectric conversion unit. The light intensity monitoring unit monitors the light intensity of the local reference light and the backscattered Rayleigh light in real time, and sends a feedback control signal to the dynamic beam splitter based on the comparison of their light intensities to adjust the beam splitting ratio to achieve optimal monitoring results. The optical mixer mixes the adjusted local reference light and the backscattered Rayleigh light and outputs an interference light signal. The photoelectric conversion unit converts the interference light signal into an electrical signal carrying acoustic information. The signal processing module is used to acquire and process the electrical signal, extract acoustic information, and identify the type and location of acoustic events.

2. The submarine cable acoustic monitoring system based on scattering fiber optic fingerprint technology according to claim 1, characterized in that, The dynamic beam splitter divides the continuous light output by the laser into probe light and local reference light according to a preset initial ratio. The preset initial ratio is that 90% of the energy of the light is used as the probe light and 10% of the energy of the light is used as the local reference light.

3. The submarine cable acoustic monitoring system based on scattering fiber optic fingerprint technology according to claim 1, characterized in that, The optical mixer performs a mixing process between the local reference light and the backscattered Rayleigh light, specifically as follows: Let the local reference photoelectric field intensity be in, For reference light amplitude, As a reference light angular frequency, The initial phase of the reference light; Suppose there is an external acoustic disturbance signal at the incident end x of the distance probe light in the optical fiber, and the electric field strength of the backscattered Rayleigh light transmitted to the input of the optical mixer is: in, Let x be the amplitude of the scattered light at the incident end of the probe light. To detect the angular frequency of light, This is the time delay for the backscattered Rayleigh light to travel to the mixer input. This refers to the dynamic phase change caused by external disturbances. The inherent scattering phase at the incident end of the probe light x is determined by the microstructure of the optical fiber and does not change with time. The total light intensity after the local reference light and the backscattered Rayleigh light are coupled by the optical mixer is: in, The intensity of the local reference light, The intensity of the backscattered Rayleigh light; The total phase difference is expressed as: because , , All of these are constants that do not change with time, and their sum is considered as a fixed bias phase. Therefore, the total phase difference simplifies to: Substituting into the total light intensity formula, the interference term light intensity is: The intensity of the interference term will affect the dynamic phase change caused by external acoustic disturbances. This is converted into periodic fluctuations in light intensity, enabling the extraction of acoustic information.

4. A submarine cable acoustic monitoring system based on scattering fiber optic fingerprint technology according to claim 1 or 3, characterized in that, The adjustment of the beam splitting ratio to achieve optimal monitoring effect means that the interference term intensity coefficient reaches its maximum value. Specifically, this is achieved through real-time monitoring by the intensity monitoring unit and feedback control by the dynamic beam splitter, ensuring that the intensity of the local reference light is adjusted accordingly. Light intensity of backscattered Rayleigh light They satisfy the equality relationship, where x is the distance between the position on the optical fiber affected by the external acoustic disturbance and the incident end of the probe light.

5. The submarine cable acoustic monitoring system based on scattering fiber optic fingerprint technology according to claim 5, characterized in that, The light intensity adjustment amount corresponding to the feedback control signal sent by the light intensity monitoring unit to the dynamic beam splitter is determined by the following formula: In the formula, The light intensity of the local reference light initially measured by the light intensity monitoring unit. The intensity of the backscattered Rayleigh light initially measured by the light intensity monitoring unit; This is the amount of light intensity adjustment; if Then adjust the dynamic beam splitter to reduce the local reference beam. Then adjust the dynamic beam splitter to increase the local reference beam.

6. The submarine cable acoustic monitoring system based on scattering fiber optic fingerprint technology according to claim 1, characterized in that, The submarine cable fiber optic sensing unit uses the existing optical fiber in the submarine cable as the sensing medium to achieve non-invasive monitoring of the submarine cable.

7. The submarine cable acoustic monitoring system based on scattering fiber optic fingerprint technology according to claim 1, characterized in that, The photoelectric conversion unit includes an InGaAs photodetector unit and a transimpedance amplifier, used to convert optical signals into voltage signals.

8. The submarine cable acoustic monitoring system based on scattering fiber optic fingerprint technology according to claim 1, characterized in that, The signal processing module includes: An analog-to-digital conversion unit is used to perform high-precision sampling and digital conversion of the electrical signal; The digital signal processing unit has a built-in phase demodulation algorithm, which is used to demodulate, filter and transform the digitized signal to extract phase information; The acoustic analysis unit has a built-in acoustic event feature library and evaluation model, which is used to identify the type, intensity, and location of acoustic events and assess the hazard level based on the extracted phase information. The feature library includes signal feature templates for ship noise, fishery operation vibration, anchor impact, and seismic waves.

9. The submarine cable acoustic monitoring system based on scattering fiber optic fingerprint technology according to claim 1, characterized in that, The laser is a semiconductor laser with a linewidth ≤ 10kHz and an output light wavelength range of 1550nm.

10. The submarine cable acoustic monitoring system based on scattering fiber optic fingerprint technology according to claim 1, characterized in that, The transmitting module includes a pulsed electro-optic modulator and a circulator; the modulation frequency range of the pulsed electro-optic modulator is 1kHz~1MHz, and the output optical pulse width adjustment range is 10ns~100ns.

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