CN110518971B - Submarine optical cable disturbance monitoring system with relay based on underwater sampling - Google Patents

Abstract

The invention relates to an underwater sampling-based submarine optical cable disturbance monitoring system with a relay, wherein a linear frequency modulated detection optical signal is connected with a downlink transmission optical fiber of a relay section through a downlink relay amplifier and an optical fiber interferometer. The backward Rayleigh scattering signals generated by the downlink transmission optical fibers of each relay section of the detection optical signals are coherent with the local optical signals in the optical fiber interferometer, the optical fiber interferometer outputs disturbance monitoring signals of the submarine optical fibers of the relay section, the disturbance monitoring signals are accessed to the sampling module of the relay section, the digital optical signals of the disturbance monitoring signals respectively occupy different DWDM wavelengths, and the digital optical signals are multiplexed into the uplink transmission optical fibers and/or the downlink transmission optical fibers through multiplexing equipment and transmitted to shore-based demodulation equipment to demodulate the disturbance monitoring signals and early warn the safety state of the submarine optical fibers of each section. The scheme is based on the OFDR technology, and realizes the disturbance monitoring of the long-span relay submarine optical cable with the distance of more than 1000 km.

Description

A submarine optical cable disturbance monitoring system with relays based on underwater sampling

Technical Field

The present invention relates to a distributed optical fiber sensing system, and in particular to a disturbance monitoring system for submarine optical cables with powered relays used for long-span physical safety monitoring.

Background technique

Submarine optical cables are communication transmission cables laid on the seabed and are an important part of the international Internet and other underwater optical networks. However, submarine optical cables are easily damaged. For example, earthquakes, anchors, fishing nets, etc. may damage submarine optical cables, and there may even be human damage. At present, each section of the relayed submarine optical cable is connected to a relay amplifier to compensate for the transmission loss of the optical signal on this section of optical fiber and amplify the optical signal to the original power level. Such relayed submarine optical cables generally use COTDR (Coherent Detection OTDR Optical Time Domain Reflectometer) to realize the health detection of the optical fiber link. It has the functions of checking the signal gain of each amplifier on the entire optical fiber link, whether the optical cable is broken, and locating the breakpoint.

However, COTDR cannot achieve the same optical cable disturbance monitoring function as φ-OTDR, and cannot provide real-time warnings for sabotage, nor can it provide technical support for stopping sabotage. The current optical cable disturbance monitoring technology used on land only supports a maximum monitoring range of about 100km, and double-end detection can only reach 200km. It cannot meet the disturbance monitoring requirements of ultra-long spans of more than 200km for submarine optical cables.

Optical frequency domain reflectometer (OFDR) is a high-resolution optical fiber measurement technology that has been gradually developed since the 1990s. It is different from the commonly used optical time domain reflectometer (OTDR). OTDR performs optical fiber diagnostic measurements by emitting time domain pulse signals, detecting pulse flight time, and using the relationship that the pulse flight time is proportional to the target distance, while OFDR performs optical fiber diagnostic measurements by emitting continuous frequency modulated laser signals, detecting the beat frequency of the target reflected light and the local oscillator light, and using the relationship that the beat frequency is proportional to the target distance. OFDR has higher sensitivity and resolution than OTDR, but OFDR's frequency modulated light source technology is difficult and costly, and the phase demodulation of the disturbance signal is difficult. Therefore, there are no reports on its use for submarine cable disturbance monitoring.

Summary of the invention

The purpose of the present invention is to provide a disturbance monitoring system for submarine optical cables with relays based on underwater sampling. Based on OFDR technology, a linear frequency modulated detection optical signal is connected to a downlink transmission optical fiber. Each section of the downlink transmission optical fiber is first connected to a relay amplifier, then connected to a fiber interferometer, and then connected to the downlink transmission optical fiber of this section. The backward Rayleigh scattering signal generated by the detection optical signal in the downlink transmission optical fiber of each relay section is coherent with the local optical signal in the fiber interferometer. The fiber interferometer outputs the disturbance monitoring signal of the submarine optical cable optical fiber of the relay section, and is connected to the sampling module of this relay section. The digital optical signals of the disturbance monitoring signal of the submarine optical fiber of each relay section respectively occupy different DWDM (Dense Wavelength Division Multiplexing) wavelengths, are multiplexed into the uplink transmission optical fiber and/or the downlink transmission optical fiber through a multiplexing device, and are transmitted to a shore-based demodulation device, which demodulates the disturbance monitoring signal and warns the safety status of each section of the submarine optical cable. This solution overcomes the shortcoming that the existing optical cable disturbance monitoring technology only supports a monitoring range of about 100 km at most, and realizes the disturbance monitoring of long-span relayed submarine optical cables with a distance of more than 1000 km.

The invention discloses a submarine optical cable disturbance monitoring system with relays based on underwater sampling, which comprises a detection light source, a relay amplifier, an optical fiber interferometer and a demodulation device. The detection light source is connected to a downlink transmission optical fiber of a submarine optical cable detection light signal. Each section of the downlink transmission optical fiber is first connected to a downlink relay amplifier. A certain transmission loss is generated when the detection light signal is transmitted through each section of the optical fiber. The relay amplifier amplifies the detection light signal to the original power level to achieve long-distance transmission. The optical fiber length between two adjacent downlink relay amplifiers is less than or equal to 100 km, which is called a relay section. A fiber interferometer is connected to the downlink relay amplifier of the downlink transmission optical fiber of each relay section, and then connected to the downlink transmission optical fiber of the detection arm of the optical fiber interferometer of this section. The system also includes a sampling module and a multiplexing device, which detects the backward Rayleigh scattering signal generated by the optical signal in the downlink transmission optical fiber of a certain relay section and is coherent with the local optical signal of the optical fiber interferometer, so as to generate a disturbance monitoring signal of the submarine optical cable optical fiber of the relay section, and connects the sampling module of this relay section through the local filter. The sampling module samples the disturbance monitoring signal and outputs its digital optical signal, which is connected to the uplink and downlink multiplexing devices and multiplexed with the digital optical signals of the disturbance monitoring signals of other relay sections in the uplink and downlink transmission optical fibers respectively, that is, enters the uplink transmission optical fiber through the uplink relay amplifier and is transmitted to the demodulation device at this end; or enters the downlink transmission optical fiber through the downlink relay amplifier and is transmitted to the demodulation device at the opposite end.

The fiber interferometer is a Michelson fiber interferometer including a 2×2 fiber coupler and a fiber reflector. The detection light signal is connected to the first port of the 2×2 fiber coupler and is divided into two beams, one of which is output from the third port of the 2×2 fiber coupler and connected to the downlink transmission fiber for further downlink transmission. The generated backward Rayleigh scattering signal is returned to the 2×2 fiber coupler from the third port; the other detection light signal separated by the 2×2 fiber coupler is output from the fourth port of the 2×2 fiber coupler to the fiber reflector, and is reflected back to the 2×2 fiber coupler as a local light signal. The local light signal is coherent with the backward Rayleigh scattering signal, and the interference signal is output from the second port of the 2×2 fiber coupler as a disturbance monitoring signal of this section of the submarine optical cable.

Or the fiber interferometer is an MZ fiber interferometer (Mach-Zehnder interferometer), including a fiber splitter, a fiber circulator and a 3dB fiber coupler. The splitting ratio of the fiber splitter is (5/95) to (50/50). The detection light signal is divided into two paths in the fiber splitter, wherein one light signal with a large splitting ratio is connected to the first port of the fiber circulator, and then output from the second port of the fiber circulator, and connected to the downstream transmission fiber for continued downstream transmission; the light signal with a small splitting ratio output by the fiber splitter is connected to the 3dB fiber coupler as a local light signal; the backward Rayleigh signal generated on the downstream transmission fiber returns to the second port of the fiber circulator, and is connected to the 3dB fiber coupler from the third port of the fiber circulator to be coherent with the local light signal, and the interference signal output by the 3dB fiber coupler is the disturbance monitoring signal of this section of the submarine optical cable.

The detection light source is a single-wavelength narrow-linewidth frequency-modulated continuous wave light source. The coherence length of the detection light signal it generates in the optical fiber is greater than twice the length of the submarine optical cable relay section, and the maximum beat frequency generated by its frequency modulation range is less than 1/2 of the maximum sampling frequency of the sampling module to meet the sampling requirements.

The digital optical signals of the disturbance monitoring signals output by the sampling modules of each relay section occupy different DWDM wavelengths respectively. The disturbance monitoring signals of the submarine optical cable of the relay section output by the optical fiber interferometers of each relay section are connected to the sampling module through filters to output the digital optical signals of the disturbance monitoring signals of the submarine optical cable of the relay section.

The detection light source, demodulation equipment, and the uplink relay amplifier, downlink relay amplifier, fiber interferometer, sampling module and multiplexing equipment of the first relay segment are all shore-based equipment at this end. The shore-based equipment at the opposite end includes the demodulation equipment at the opposite end.

Another solution is that the detection light signal emitted by the detection light source and other communication light signals emitted by the shore-based optical terminal are all connected to the wavelength division multiplexer, and the wavelength division multiplexing is used for downlink transmission on the same optical fiber of the submarine optical cable. The digital light signal of the disturbance monitoring signal output by the sampling module is connected to the downlink optical add-drop multiplexer of this relay section, multiplexed with the digital light signals of the disturbance monitoring signals of other relay sections and other communication signals to the downlink transmission optical fiber, and transmitted to the demodulation equipment at the opposite end; at the same time, the digital light signal of the disturbance monitoring signal output by the sampling module is connected to the uplink optical add-drop multiplexer of this relay section, multiplexed with the digital light signals of the disturbance monitoring signals of other relay sections and other communication signals to the uplink transmission optical fiber, and transmitted back to the demodulation equipment at this end.

Another scheme is that the detection light signal emitted by the detection light source and other communication light signals emitted by the shore-based optical terminal are all connected to the wavelength division multiplexer and multiplexed for downlink transmission on the same optical fiber of the submarine optical cable. A certain relay section is equipped with an underwater node communication module and connected to the underwater equipment, that is, the underwater node. The digital light signal of the disturbance monitoring signal output by the sampling module is connected to the underwater node communication module and time-division multiplexed with other communication signals of the underwater equipment of the underwater node. The underwater node communication module is connected to the downlink optical add-drop multiplexer of this relay section, and its output signal is wavelength-division multiplexed with other communication light signals to the downlink transmission optical fiber, and transmitted to the optical terminal at the opposite end. The optical terminal at the opposite end demultiplexes the disturbance monitoring signal and sends it to the demodulation device at the opposite end. At the same time, the underwater node communication module is connected to the uplink optical add-drop multiplexer of this relay section, and its output signal is wavelength-division multiplexed with other communication light signals to the uplink transmission optical fiber, and is transmitted back to the optical terminal at this end. The optical terminal at this end demultiplexes the disturbance monitoring signal and sends it to the demodulation device at this end.

This system adds a disturbance monitoring branch for the branch submarine optical cable. The trunk submarine optical cable is connected to a 1×2 optical fiber splitter at a certain underwater node, and the detection optical signal is divided into two paths. One path continues to be transmitted downstream along the downlink transmission optical fiber of the trunk submarine optical cable, and the other path is connected to the branch cable optical fiber interferometer. After passing through the branch cable optical fiber interferometer, the detection optical signal continues to be transmitted downstream along the branch submarine optical cable. The backward Rayleigh scattering signal generated on the branch submarine optical cable is coherent with its local optical signal in the branch cable optical fiber interferometer to obtain the disturbance monitoring signal of this section of the branch submarine optical cable. The disturbance monitoring signal of the branch submarine optical cable is connected to the branch cable sampling module through the branch cable filter. The digital optical signal of the disturbance monitoring signal output by the sampling module on the trunk submarine optical cable and the digital optical signal of the branch submarine optical cable disturbance monitoring signal output by the branch cable sampling module are both connected to the underwater node communication module to aggregate data and perform time division multiplexing. The digital optical signal synthesized by the underwater node communication module is connected to the downlink optical add-drop multiplexer of this relay section and the uplink optical add-drop multiplexer of this relay section.

Compared with the prior art, the submarine optical cable disturbance monitoring system with relay based on underwater sampling and the operation method of the present invention have the following beneficial effects: 1. Based on OFDR technology, the problem that the submarine optical cable disturbance monitoring system cannot penetrate the submarine repeater is overcome, and the detection distance of the submarine optical cable disturbance monitoring system is increased from less than 100km to thousands of kilometers, meeting the requirements of real-time monitoring of the physical safety of long-span submarine optical cables; 2. It supports disturbance monitoring of branch submarine optical cables.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a schematic structural diagram of Embodiment 1 of the submarine optical cable disturbance monitoring system with relays based on underwater sampling;

FIG2 is a schematic diagram of the structure of a Michelson fiber interferometer of Example 1 of the submarine optical cable disturbance monitoring system with relay based on underwater sampling;

FIG3 is a schematic diagram of the structure of an MZ fiber interferometer of Example 2 of the submarine optical cable disturbance monitoring system with relays based on underwater sampling;

FIG4 is a schematic structural diagram of Embodiment 2 of the submarine optical cable disturbance monitoring system with relays based on underwater sampling;

FIG5 is a schematic structural diagram of Embodiment 3 of the submarine optical cable disturbance monitoring system with relays based on underwater sampling;

FIG6 is a schematic structural diagram of Embodiment 4 of the submarine optical cable disturbance monitoring system with relays based on underwater sampling.

Detailed ways

Example 1 of a submarine optical cable disturbance monitoring system with relays based on underwater sampling

In the embodiment 1 of the submarine optical cable disturbance monitoring system with relay based on underwater sampling, FIG1 shows a certain relay segment, the shore-based equipment at this end and the demodulation equipment at the other end. The detection light source is first connected to a downlink relay amplifier, the downlink EDFA in the figure, and the downlink relay amplifier downlink EDFA of each relay segment downlink transmission optical fiber is connected to the fiber interferometer, and then connected to the downlink transmission optical fiber of the detection arm of the fiber interferometer of this segment. In this example, the optical fiber length between two adjacent downlink relay amplifiers is 60 to 100 km, which is called a relay segment.

The back Rayleigh scattering signal generated by the detection optical signal in the downlink transmission optical fiber of a certain relay section is coherent with the local optical signal of the optical fiber interferometer to generate a disturbance monitoring signal of the submarine optical cable optical fiber of the relay section, which is connected to the sampling module of this relay section through the local filter. The sampling module samples the disturbance monitoring signal and outputs its digital optical signal, which is connected to the downlink multiplexing device - the downlink optical add/drop multiplexer downlink OADM and the uplink multiplexing device - the uplink optical add/drop multiplexer uplink OADM, and is multiplexed with the digital optical signals of the disturbance monitoring signals of other relay sections in the uplink and downlink transmission optical fibers respectively, that is, enters the uplink transmission optical fiber through the uplink EDFA of the uplink relay amplifier and is transmitted to the demodulation device at the local end; or enters the downlink transmission optical fiber through the downlink EDFA of the downlink relay amplifier and is transmitted to the demodulation device at the opposite end.

The fiber interferometer in this example is a Michelson fiber interferometer including a 2×2 fiber coupler and a fiber reflector, and its structure is shown in Figure 2. The detection light signal is connected to the first port of the 2×2 fiber coupler and is divided into two beams, one of which is connected to the downlink transmission fiber through the third port of the 2×2 fiber coupler for further downlink transmission, and the generated backward Rayleigh scattering signal is returned to the 2×2 fiber coupler through the third port; the other detection light signal separated by the 2×2 fiber coupler is output from the fourth port of the 2×2 fiber coupler to the fiber reflector, which is reflected back to the 2×2 fiber coupler as a local light signal. The local light signal is coherent with the backward Rayleigh scattering signal, and the interference signal is output from the second port of the 2×2 fiber coupler as a disturbance monitoring signal of this section of the submarine optical cable.

The detection light source in this example is a single-wavelength narrow-linewidth frequency-modulated continuous wave light source. The coherence length of the detection light signal it generates in the optical fiber is greater than twice the length of the submarine optical cable relay section, and the maximum beat frequency generated by its frequency modulation range is less than 1/2 of the maximum sampling frequency of the sampling module.

The digital optical signals of the disturbance monitoring signals output by the sampling modules of each relay section occupy different wavelengths respectively. The disturbance monitoring signals of the submarine optical cable of the relay section output by the optical fiber interferometers of each relay section are connected to the sampling module through filters to output the digital optical signals of the disturbance monitoring signals of the submarine optical cable of the relay section.

In this example, the detection light source, demodulation equipment, and the uplink relay amplifier uplink EDFA, downlink relay amplifier downlink EDFA, fiber interferometer, sampling module, and downlink multiplexing equipment downlink optical add/drop multiplexer downlink OADM of the first relay segment are all shore-based equipment at this end. The shore-based equipment at the opposite end includes the demodulation equipment at the opposite end.

Example 2 of a submarine optical cable disturbance monitoring system with relays based on underwater sampling

Fig. 4 shows a certain relay section, the shore-based equipment at this end and the demodulation equipment at the opposite end of this example. The main structure of this example is the same as that of Example 1, except that the detection light signal emitted by the detection light source and other communication light signals are connected to the wavelength division multiplexer, and the wavelength division multiplexing is used for the same optical fiber of the submarine optical cable for downlink transmission. The digital light signal of the disturbance monitoring signal output by the sampling module is connected to the downlink optical add-drop multiplexer downlink OADM of this relay section and multiplexed with the digital light signal of the disturbance monitoring signal of other relay sections and other communication signals emitted by the shore-based optical terminal to the downlink transmission optical fiber, and then transmitted to the demodulation equipment at the opposite end; at the same time, the digital light signal of the disturbance monitoring signal output by the sampling module is connected to the uplink optical add-drop multiplexer uplink OADM of this relay section and multiplexed with the digital light signal of the disturbance monitoring signal of other relay sections and other communication signals to the uplink transmission optical fiber, and then transmitted back to the demodulation equipment at this end.

The fiber interferometer in this example is an MZ fiber interferometer, as shown in FIG3 , and includes a fiber splitter, a fiber circulator and a 3dB fiber coupler. The splitting ratio of the fiber splitter is 10/90. The detection optical signal is divided into two paths in the fiber splitter, wherein one optical signal with a large splitting ratio is connected to the first port of the fiber circulator, and then outputted from the second port of the fiber circulator, and connected to the downlink transmission optical fiber for further downlink transmission; the optical signal with a small splitting ratio outputted by the fiber splitter is connected to the 3dB fiber coupler as a local optical signal; the backward Rayleigh signal generated on the downlink transmission optical fiber is returned to the second port of the fiber circulator, and connected to the 3dB fiber coupler by the third port of the fiber circulator to be coherent with the local optical signal, and the interference signal outputted by the 3dB fiber coupler is the disturbance monitoring signal of this section of the submarine optical cable.

Example 3 of a submarine optical cable disturbance monitoring system with relays based on underwater sampling

FIG5 shows a relay section and the shore-based equipment at this end in this example. The main structure of this example is the same as that of Example 2. The detection light signal emitted by the detection light source in this example and other communication light signals emitted by the shore-based optical terminal are connected to the wavelength division multiplexer, and the wavelength division multiplexing is used for the same optical fiber of the submarine optical cable for downlink transmission. The digital light signal of the disturbance monitoring signal output by the sampling module is connected to the underwater node communication module for time division multiplexing with other communication signals of the underwater equipment. The underwater node communication module is connected to the downstream OADM of the downlink optical add-drop multiplexer of this relay section, and its output signal is wavelength-division multiplexed with other communication light signals to the downlink transmission optical fiber, and transmitted to the optical terminal at the opposite end. The optical terminal at the opposite end demultiplexes the disturbance monitoring signal and sends it to the demodulation equipment at the opposite end; at the same time, the underwater node communication module is connected to the upstream OADM of the uplink optical add-drop multiplexer of this relay section, and its output signal is wavelength-division multiplexed with other communication light signals to the uplink transmission optical fiber, and is transmitted back to the optical terminal at this end. The optical terminal at this end demultiplexes the disturbance monitoring signal and sends it to the demodulation equipment at this end.

Example 4 of a submarine optical cable disturbance monitoring system with relays based on underwater sampling

FIG6 shows a relay section and underwater node communication module of this example. This example adds a disturbance monitoring branch of a branch submarine cable on the basis of Example 3. An underwater node of the trunk submarine cable is connected to a 1×2 optical fiber splitter, and the detection optical signal is divided into two paths, one of which continues to be transmitted downstream along the downlink transmission optical fiber of the trunk submarine cable, and the other is connected to the branch cable optical fiber interferometer. The detection optical signal continues to be transmitted downstream along the branch submarine cable after passing through the branch cable optical fiber interferometer. The backward Rayleigh scattered signal generated on the branch submarine cable is coherent with its local optical signal in the branch cable optical fiber interferometer to obtain the disturbance monitoring signal of this section of the branch submarine cable. The disturbance monitoring signal of the branch submarine cable is connected to the branch cable sampling module through the branch cable filter. The underwater node connected to the branch submarine cable is equipped with an underwater node communication module. The digital optical signal of the disturbance monitoring signal output by the sampling module on the trunk submarine cable and the digital optical signal of the branch submarine cable disturbance monitoring signal output by the branch cable sampling module are both connected to the underwater node communication module to aggregate data and perform time division multiplexing. The digital optical signal synthesized by the underwater node communication module is connected to the downlink optical add-drop multiplexer OADM of this relay section and the uplink optical add-drop multiplexer uplink OADM of this relay section.

The above embodiments are only specific examples for further describing the purpose, technical solutions and beneficial effects of the present invention, and the present invention is not limited thereto. Any modification, equivalent replacement, improvement, etc. made within the scope of the disclosure of the present invention are included in the protection scope of the present invention.

Claims (7)

1. The system comprises a detection light source, a relay amplifier, an optical fiber interferometer and demodulation equipment, wherein the detection light source is connected with a downlink transmission optical fiber of a submarine optical cable detection optical signal, and each section of the downlink transmission optical fiber is connected with one relay amplifier; the length of the optical fiber between the two relay amplifiers is less than or equal to 100km, which is called a relay; the relay amplifier of each relay section downlink transmission optical fiber is connected with an optical fiber interferometer, and then is connected with the downlink transmission optical fiber serving as a detection arm of the optical fiber interferometer; the method is characterized in that:

the system also comprises a sampling module and multiplexing equipment, wherein the backward Rayleigh scattering signal generated by the downlink transmission optical fiber of a certain relay segment of the detected optical signal is coherent with the local optical signal of the optical fiber interferometer, the disturbance monitoring signal of the submarine optical cable optical fiber of the relay segment is generated, the disturbance monitoring signal is accessed to the sampling module of the relay segment through the filter of the segment, the digital optical signal is output after the sampling module samples the disturbance monitoring signal, the digital optical signal is accessed to the multiplexing equipment, and the digital optical signal of the disturbance monitoring signal of other relay segments is multiplexed to the uplink transmission optical fiber and the downlink transmission optical fiber respectively, namely enters the uplink transmission optical fiber through the uplink relay amplifier, is transmitted to the optical terminal of the local end, and is accessed to the demodulation equipment after the demultiplexing; or the optical fiber enters a downlink transmission optical fiber through a downlink relay amplifier and is transmitted to an optical transceiver of the opposite terminal, and the optical transceiver is connected to demodulation equipment of the opposite terminal after demultiplexing;

The detection light source is a single-wavelength narrow-linewidth frequency modulation continuous wave light source, the coherence length of the generated detection light signal in the optical fiber is more than 2 times of the length of the submarine optical cable relay section, and the maximum beat frequency generated in the frequency modulation range is less than 1/2 of the maximum sampling frequency of the sampling module;

The digital optical signals of disturbance monitoring signals output by the sampling module of each relay segment occupy different wavelengths respectively, the disturbance monitoring signals of the submarine cable of the relay segment output by the optical fiber interferometer of each relay segment are connected into the sampling module through a filter, and the digital optical signals of the disturbance monitoring signals of the submarine cable of the relay segment are output.

2. The undersea optical fiber cable disturbance monitoring system with relay based on underwater sampling according to claim 1, wherein:

The optical fiber interferometer is a Michelson optical fiber interferometer comprising a 2 x 2 optical fiber coupler and an optical fiber reflector; the 1 st port of the 2X 2 optical fiber coupler is connected with the detection optical signal and is divided into 2 beams, wherein one beam is connected with the downlink transmission optical fiber through the 3 rd port of the 2X 2 optical fiber coupler to continue downlink transmission, and the generated backward Rayleigh scattering signal is returned to the 2X 2 optical fiber coupler through the 3 rd port; the other beam of detection light signals split by the 2X 2 optical fiber coupler is output by the 4 th port of the 2X 2 optical fiber coupler to reach the optical fiber reflector, and is reflected back to the 2X 2 optical fiber coupler to serve as a local light signal, the local light signal is coherent with the backward Rayleigh scattering signal, and the interference signal is output by the 2 nd port of the 2X 2 optical fiber coupler to serve as a disturbance monitoring signal of the submarine optical cable;

Or the optical fiber interferometer is an MZ optical fiber interferometer and comprises an optical fiber branching device, an optical fiber circulator and a 3dB optical fiber coupler, wherein the optical splitting ratio of the optical fiber branching device is 5/95-50/50, a detection optical signal is divided into 2 paths at the optical fiber branching device, one path of optical signal with a large optical splitting ratio is connected to a first port of the optical fiber circulator, and then is output by an optical fiber annular second port, and is connected to a downlink transmission optical fiber to continue downlink transmission; the optical signal with small splitting ratio output by the optical fiber splitter is used as a local optical signal to be connected into a 3dB optical fiber coupler; and a backward Rayleigh signal generated on the downlink transmission optical fiber is returned to the second port of the optical fiber circulator, the third port end of the optical fiber circulator is connected into the 3dB optical fiber coupler to be coherent with a local optical signal, and an interference signal output by the 3dB optical fiber coupler is a disturbance monitoring signal of the submarine optical cable of the section.

3. The undersea optical fiber cable disturbance monitoring system with relay based on underwater sampling according to claim 1, wherein:

The detection light source is a single-wavelength narrow-linewidth frequency modulation continuous wave light source, the coherence length of the generated detection light signal in the optical fiber is greater than 2 times of the length of the submarine optical cable relay section, and the maximum beat frequency generated in the frequency modulation range is less than 1/2 of the maximum sampling frequency of the sampling module;

the digital optical signals of disturbance monitoring signals output by the sampling module of each relay are respectively occupied by different DWDM wavelengths, and the disturbance monitoring signals of the submarine optical cable of the relay output by the optical fiber interferometer of each relay are connected into the sampling module through a filter to output the digital optical signals of the disturbance monitoring signals of the submarine optical cable of the relay.

4. The undersea optical fiber cable disturbance monitoring system with relay based on underwater sampling according to claim 1, wherein:

The detection light source, the demodulation equipment, the uplink relay amplifier, the downlink relay amplifier, the optical fiber interferometer, the sampling module and the multiplexing equipment of the first relay section are local terminal shore-based equipment; the opposite bank-based device includes an opposite demodulation device.

5. The undersea optical fiber cable with relay and based on underwater sampling according to any one of claims 1 to 4, wherein:

the digital optical signals of disturbance monitoring signals output by the sampling module are connected to the downlink optical add drop multiplexer of the relay section and other communication signals to be multiplexed to a downlink transmission optical fiber and transmitted to demodulation equipment of an opposite end; meanwhile, the digital optical signal of the disturbance monitoring signal output by the sampling module is accessed into the uplink optical add-drop multiplexer of the trunk and other communication signals to be multiplexed to the uplink transmission optical fiber and returned to the demodulation equipment of the local end.

6. The undersea optical fiber cable with relay and based on underwater sampling according to any one of claims 1 to 4, wherein:

The detection light signal sent by the detection light source and other communication light signals emitted by the shore-based optical terminal machine are subjected to wavelength division multiplexing on the same optical fiber of the submarine optical cable for downlink transmission, a certain relay section is provided with an underwater node communication module and is connected with underwater equipment, namely, the underwater node is connected with the digital light signal of the disturbance monitoring signal output by the sampling module, the digital light signal is connected with the underwater node communication module for time division multiplexing with other communication signals of the underwater node underwater equipment, the underwater node communication module is connected with a downlink optical add/drop multiplexer of the relay section, the output signal and other communication light signals are subjected to wavelength division multiplexing to a downlink transmission optical fiber and transmitted to an optical terminal machine at the opposite end, and the optical terminal machine at the opposite end demultiplexes the disturbance monitoring signal and then sends the disturbance monitoring signal to demodulation equipment at the opposite end; meanwhile, the underwater node communication module is connected with the uplink optical add/drop multiplexer of the relay, the output signal and other communication optical signals are multiplexed to the uplink transmission optical fiber in a wavelength division manner and transmitted back to the optical terminal of the local terminal, and the optical terminal of the local terminal demultiplexes the disturbance monitoring signal in a time division manner and then transmits the disturbance monitoring signal to the demodulation equipment of the local terminal.

7. The undersea optical fiber cable with relay and based on underwater sampling according to any one of claims 1 to 4, wherein:

The system is added with disturbance monitoring branches of the branched sea optical cable; a certain relay is provided with an underwater node communication module and is connected with underwater equipment, namely an underwater node, a certain underwater node of a main submarine optical cable is connected with a 1X 2 optical fiber branching device, a detection optical signal is divided into 2 paths, one path of detection optical signal continues to be transmitted downwards along a downlink transmission optical fiber of the main submarine optical cable, the other path of detection optical signal is connected with a branch cable optical fiber interferometer, the detection optical signal continues to be transmitted downwards along a branch submarine optical cable after passing through the branch cable optical fiber interferometer, a backward Rayleigh scattering signal generated on the branch submarine optical cable is coherent with a local optical signal of the branch submarine optical cable in the branch cable optical fiber interferometer to obtain a disturbance monitoring signal of the branch submarine optical cable, and the disturbance monitoring signal of the branch submarine optical cable is connected into a branch cable sampling module through a branch cable filter; the digital optical signals of the disturbance monitoring signals output by the sampling module on the main sea optical cable and the digital optical signals of the disturbance monitoring signals output by the branch sea optical cable sampling module are connected into the underwater node communication module to gather data and perform time division multiplexing, and the digital optical signals synthesized by the underwater node communication module are connected into the downlink optical add/drop multiplexer of the underwater node and the uplink optical add/drop multiplexer of the underwater node.