A repeater submarine optical fiber cable vibration monitoring system based on time and space division multiplexing

Abstract

To provide a relay submarine fiber optic cable vibration monitoring system based on time division and spatial division multiplexing.SOLUTION: In a system, a detection light source is connected to a downlink relay amplifier and a fiber optic interferometer, and is connected to a next downlink relay amplifier via a downlink transmission optical fiber in this section. A detection optical signal generates a rear Rayleigh scattered signal on a transmitted optical fiber of each section, and the rear Rayleigh scattered signal interferes with a local optical signal by the optical fiber interferometer, and generates a vibration monitoring signal for a submarine optical fiber cable in this section. The vibration monitoring signal enters one of uplink transmission fiber optics through a filter and a fiber optic coupler and is returned to a demodulator. The demodulator distinguishes the vibration monitoring signal for each section by a difference between the uplink optical fiber and a pulse rise edge time, and promptly warns and analyzes the condition of the submarine optical fiber cable in each section.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a distributed optical fiber sensing system, in particular to a repeater submarine optical fiber cable vibration monitoring system based on time division and space division multiplexing, which combines time division and space division multiplexing of uplink transmission vibration monitoring signals and is used for long-distance physical security monitoring and detection by land-based facilities. [Background technology]

[0002] Submarine fiber optic cables are communication transmission cables deployed on the ocean floor and are an important part of the Internet and other underwater optical networks. However, submarine fiber optic cables are easily damaged and can be damaged by things like earthquakes, ship anchors, and fishing nets, or even by humans. Currently, in an electrically repeating submarine fiber optic cable, each optical fiber section is connected to a repeating amplifier to compensate for the optical signal transmission attenuation over this section and to amplify the optical signal to its original power level. In this type of electrically repeating submarine fiber optic cable, a COTDR (Coherent Optical Time Domain Reflectometer) is generally used to detect the health of the optical fiber link. The COTDR monitors the signal gain of each amplifier over the entire optical fiber link and functions to find the presence and location of breaks in the optical fiber cable.

[0003] However, COTDR cannot achieve the same optical fiber cable vibration monitoring function as Φ-OTDR, and therefore will not provide real-time warning of sabotage and therefore technical assurance to stop the sabotage.

[0004] Current optical fiber cable vibration monitoring technologies used on land can only support a maximum monitoring range of about 100 km, and double-ended detection can only reach 200 km, which cannot extend beyond the repeater amplifiers for submarine optical fiber cables and cannot meet the requirements of electrically repeatered submarine optical fiber cables for extremely long monitoring ranges.

[0005] Optical frequency domain reflectometer (OFDR) was gradually developed in the 1990s and utilizes high-resolution optical fiber measurement technology. The commonly used optical time domain reflectometer (OTDR) transmits a time domain pulse signal, detects the pulse travel time, and utilizes the proportional relationship between the pulse travel time and the target distance to perform optical fiber diagnostic measurement. Unlike OTDR, OFDR transmits a continuously frequency modulated laser signal, detects the beat frequency between the reflected light and the local oscillator light at the target, and utilizes the proportional relationship between the beat frequency and the target distance to perform optical fiber diagnostic measurement. OFDR has higher sensitivity and higher resolution than OTDR. However, in OFDR, the frequency modulated light source technology is difficult and expensive, and the phase demodulation of the vibration signal is also difficult. At present, there are no reports on the use of OFDR in submarine optical fiber cable vibration monitoring.

[0006] The currently developed repeater submarine optical fiber cable vibration monitoring system based on underwater sampling adopts OFDR technology. The detection optical signal output by the light source located on land is transmitted in the downlink through the repeater, and the vibration of the submarine optical fiber cable is segmented and detected, and each section uses a digital sampling backhaul. In this way, vibration monitoring of an electrically repeatered submarine optical fiber cable with a long section of more than 1000 km is realized. Compared with the OTDR extension technology, the repeater submarine optical fiber cable vibration monitoring system for underwater sampling using frequency modulation continuous wave technology has high average power, high signal-to-noise ratio in terms of optical signal amplification, and is suitable for long-distance detection via repeaters. However, the use of digital sampling backhaul requires the addition of an active module to the undersea repeater amplifier or underwater node, which reduces the reliability of the undersea repeater or underwater node.

[0007] The currently developed repeater submarine optical fiber cable vibration monitoring system based on detection by land facilities uses a multi-wavelength frequency modulated pulse light source to generate a downlink detection optical signal and directly return an analog optical signal for vibration monitoring. Adjacent sections not only perform time division multiplexing of the vibration monitoring signal, but also perform uplink transmission by alternately selecting the wavelength of the vibration monitoring signal. This technology avoids the problems of beat spectrum and optical wavelength overlap for the vibration monitoring optical signal of each section as well as the inability to multiplex a single fiber. In this technology, only a few optical wavelength channels of a pair of optical fibers are occupied to realize vibration monitoring of the repeater section of the submarine cable in the DWDM manner. However, it has a problem that the cost of the submarine optical fiber cable vibration monitoring device is high because it must configure and use a multi-wavelength frequency modulated pulse light source. Summary of the Invention

[0008] The objective of the present invention is to provide a repeater submarine optical fiber cable vibration monitoring system based on time division and space division multiplexing. The electrical repeater submarine optical fiber cable vibration monitoring system based on time division and space division multiplexing adopts OFDR technology. The detection light source outputs a frequency-modulated pulsed optical signal and is connected to a downlink transmission optical fiber. The downlink transmission optical fiber of each repeater section is connected to a downlink repeater amplifier, then to an optical fiber interferometer, and then to a downlink repeater amplifier of the next section through a downlink transmission optical fiber. The detection optical signal generates a backward Rayleigh scattering signal in the downlink transmission optical fiber of each repeater section, and the backward Rayleigh scattering signal interferes with the local optical signal in the optical fiber interferometer to generate a vibration monitoring signal for the submarine optical fiber cable of this repeater section. The vibration monitoring signal is input to a filter of this repeater section, then enters one of the uplink transmission optical fibers through the optical fiber coupler of this repeater section, then enters an uplink repeater amplifier connected to this uplink transmission optical fiber of this section, and finally returns to the demodulator through the uplink optical fiber. The frequency-modulated laser pulse width is n times the round trip delay time for the submarine cable of the repeater section. The uplink transmission optical fiber includes at least n uplink optical fibers, and the vibration monitoring signal for each repeater section of the submarine optical fiber cable is returned by using space division multiplexing in the n uplink optical fibers. Due to the difference in the uplink optical fibers and the pulse rising edge time, the demodulator distinguishes the vibration monitoring signal for each section, analyzes and demodulates the data, and provides early warning of the safety status of the submarine optical fiber cable of each repeater section. The present invention realizes the segmented detection of the vibration of the submarine optical fiber cable, and directly returns the vibration monitoring signal to the demodulator located on land by time division and space-time division multiplexing, thus achieving the segmented vibration monitoring and positioning of the submarine optical fiber cable of more than 1000 km.

[0009] The present invention provides a repeater submarine optical fiber cable vibration monitoring system based on time division and space division multiplexing, the system includes a detection light source, a repeater amplifier, a downlink transmission optical fiber, an optical fiber interferometer, an uplink transmission optical fiber, and a demodulator, the detection light source outputs a detection optical signal and is connected to the downlink transmission optical fiber of the submarine optical fiber cable, the downlink transmission optical fiber of each section is first connected to a downlink repeater amplifier which amplifies the detection optical signal to a power level at the detection light source to ensure long-distance transmission, the downlink repeater amplifier is then connected to an optical fiber interferometer and then to the downlink transmission optical fiber of the next section, the optical fiber length between two adjacent downlink repeater amplifiers is 100 km or less, which is called a repeater section, each repeater section of the system further includes a filter and an optical fiber coupler, the transmission wavelength of the filter is consistent with the center wavelength of the detection optical signal, the detection light source is a narrow-linewidth frequency-modulated pulse light source, the frequency-modulated pulse width of the detection optical signal is n times the round-trip delay time of one repeater section for the submarine optical fiber cable, n is an integer ranging from 2 to 8, and the frequency the modulation pulse period exceeds the round trip delay time for the entire length of the relay submarine optical fiber cable to be monitored, the uplink transmission optical fiber of each relay section includes at least n uplink optical fibers, the detection optical signal output by the detection light source is branched into two beams after entering the optical fiber interferometer of a particular relay section, one beam is transmitted downlink along the downlink transmission optical fiber of this section, and the other beam is used as a local optical signal, the backward Rayleigh scattering signal generated in the downlink transmission optical fiber of this relay section interferes with the local optical signal in the optical fiber interferometer to generate a vibration monitoring signal for the submarine optical fiber cable of this relay section, the vibration monitoring signal output by the optical fiber interferometer of this relay section is input to a filter of this relay section, and the filter transmits only the vibration monitoring signal, and the output end of the filter is connected to one of the uplink transmission optical fibers through the optical fiber coupler of this relay section, and then to an uplink relay amplifier connected to the uplink optical fiber.The vibration monitoring signals of n consecutive repeater sections are returned in sequence through the first to nth uplink transmission optical fibers, and the vibration monitoring signals of the next n consecutive repeater sections are also returned in sequence through the first to nth uplink optical fibers, so as to avoid overlapping in the time domain of adjacent vibration monitoring signals in the same uplink transmission optical fiber. The vibration monitoring signals for each repeater section returned through the uplink transmission optical fiber are respectively digitally sampled through n sampling channels of the uplink sampling device, and then transmitted to a demodulation device, where the sampling device includes an opto-electrical conversion module and an analog-to-digital conversion module, in which the optical signal is converted into an electrical signal through opto-electrical conversion, and then into a digital signal through analog-to-digital conversion. The demodulation device distinguishes the vibration monitoring signals of each repeater section, analyzes and demodulates the data, and provides an early warning of the safety status of the submarine optical fiber cable of each repeater section.

[0010] The coherent heterodyne integration time of the backscattered Rayleigh scattering signal at each point of the downlink transmission optical fiber of each repeater section is inversely proportional to the distance to each optical fiber interferometer at that point. Therefore, the longer the distance, the shorter the coherent heterodyne integration time, which is disadvantageous for vibration detection of optical fibers far from the optical fiber interferometer in the repeater section. Therefore, the present invention adopts a solution that combines time division multiplexing and space division multiplexing.

[0011] The backward Rayleigh scattering signal generated by the detection optical signal in the downlink transmission optical fiber of a particular repeater section interferes with the local optical signal. The pulse rising edge of the detection optical signal enters the optical fiber interferometer, and the vibration monitoring optical signal is output. The situation where the pulse falling edge of the detection optical signal enters the optical fiber interferometer corresponds to the situation where the local optical signal is no longer present. Therefore, the vibration monitoring signal generated by the interference is a pulse signal having the same pulse width as the pulse width of the detection optical signal output from the detection light source. Since the pulse width exceeds the round trip delay time for the submarine optical fiber cable of one repeater section, it is guaranteed that the backward Rayleigh scattering signal in the farthest part of the submarine optical fiber cable of a particular repeater section can also be received coherently.

[0012] The uplink transmission optical fiber includes at least n uplink optical fibers, and there are n uplink optical fibers involved in the uplink transmission of the vibration detection signal to the submarine optical fiber cable, where n is a multiple of the quotient of the pulse width of the detection optical signal divided by the round trip delay time of the submarine optical fiber cable of one repeater section. The filters of the first to nth repeater sections transmit the resulting vibration monitoring signal to each section, the filter of one section is connected to the 1×2 optical fiber coupler of this section, and the 1×2 optical fiber coupler of the Xth repeater section is connected to the Yth uplink optical fiber for beam combining, where Y=Xmod n, that is, Y is the remainder obtained by dividing X by n, and if Y≠0 and X is divisible by n, then Y=n. The vibration monitoring signals for different repeater sections in the same uplink optical fiber have different pulse delay times due to the difference in the positions of the repeater sections. There is a round trip delay time difference for one repeater section between the rising edges of the vibration monitoring signal pulses for adjacent repeater sections. In the present invention, the vibration monitoring pulse signals for the first to nth repeater sections are transmitted through the first to nth uplink transmission optical fibers, thereby avoiding the overlap of the vibration monitoring pulse signals in the time domain under the condition that the vibration monitoring signals have the same wavelength and the pulse width exceeds the pulse delay time difference for the adjacent repeater sections. That is, the vibration monitoring signals for each repeater section are multiplexed in n uplink optical fibers by space division and time division multiplexing. Due to the difference in the uplink optical fibers and pulse rise times, the demodulator distinguishes the vibration monitoring signals for different repeater sections.

[0013] The downlink repeater amplifier, the optical fiber interferometer, the filter, the optical fiber coupler, and the uplink repeater amplifier in the first repeater section, as well as the detection light source, the sampling device, and the demodulation device, are local devices located on land.

[0014] The optimal solution is n=2, where the frequency-modulated pulse width of the detected optical signal is twice the round trip delay time for the submarine optical fiber cable of one repeater section, the uplink transmission optical fiber includes at least two uplink optical fibers, the filter of one section is connected to the 1×2 optical fiber coupler of this section, and the 1×2 optical fiber coupler is connected to the uplink optical fiber connected to the filter of the repeater section only one repeater section away from this repeater section for beam combining.

[0015] The pulse width of the detection light source is slightly less than n times the round trip delay time for the repeater section, and the difference between the pulse width and n times the round trip delay time for the repeater section ranges from 20 nanoseconds to 1 microsecond, so that a constant time gap is maintained between the detection light signal pulses for adjacent repeater sections, thereby avoiding overlapping of the vibration monitoring signal pulses for adjacent repeater sections and facilitating the discrimination of the vibration monitoring signals for different repeater sections.

[0016] The optical fiber interferometer is an MZ optical fiber interferometer (Mach-Zehnder optical fiber interferometer), and includes an optical fiber splitter having a branching ratio of (5 / 95) to (50 / 50), an optical fiber circulator, and a 3 dB optical fiber coupler. In the optical fiber splitter, the detection optical signal is branched into two paths, the detection optical signal having a large branching ratio is input to a first port of the optical fiber circulator, then output from a second port of the optical fiber circulator, and then input to a downlink transmission optical fiber to continue downlink transmission, and the detection optical signal having a small branching ratio is input to the 3 dB optical fiber coupler as a local optical signal, and the backward Rayleigh signal generated in the downlink transmission optical fiber is returned to the optical fiber circulator through the second port of the optical fiber circulator, then input to the 3 dB optical fiber coupler through a third port of the optical fiber circulator to interfere with the local optical signal, and the 3 dB optical fiber coupler outputs a submarine optical fiber cable vibration monitoring signal for the downlink transmission optical fiber of this relay section.

[0017] In the MZ optical fiber interferometer, in the interference arm for the local oscillator light from the optical fiber splitter to the 3 dB optical fiber coupler, the optical fiber splitter is connected to a depolarizer before being connected to the 3 dB optical fiber coupler, and in the interference arm for the backward Rayleigh scattering signal from the optical fiber circulator to the 3 dB optical fiber coupler, the optical fiber circulator is connected to a depolarizer before being connected to the 3 dB optical fiber coupler. Therefore, the effect of polarization modulation is reduced and the coherence characteristics are improved.

[0018] This system is added with a vibration monitoring branch for a branch submarine optical fiber cable, and the trunk submarine optical fiber cable of a specific repeater section is connected to the branch submarine optical fiber cable, and accordingly, the uplink transmission optical fiber is added with one or two uplink optical fibers for transmitting a vibration monitoring signal to the branch submarine optical fiber cable, and in the 1×2 optical fiber splitter for the downlink transmission optical fiber, the detection optical signal is split into two paths, and in one path, the detection optical signal continues downlink transmission along the downlink transmission optical fiber and enters the optical fiber interferometer of this repeater section, and in the other path, the detection optical signal enters the optical fiber interferometer of the branch submarine cable. and then continuously transmitted along the branch submarine optical fiber cable by a downlink, and the back Rayleigh scattering signal generated in the branch submarine optical fiber cable interferes with the local optical signal in the branch submarine cable optical fiber interferometer to obtain a vibration monitoring signal for the branch submarine optical fiber cable, and the vibration monitoring signal for the branch submarine optical fiber cable is transmitted and filtered via the branch cable filter, and then input to an uplink optical fiber for transmitting the vibration monitoring signal for the branch submarine optical fiber cable through a 1×2 optical fiber coupler of the trunk submarine optical fiber cable, and then transmitted by an uplink to a sampling device arranged on land, and then input to a demodulation device.

[0019] When the trunk submarine optical fiber cable is connected to N branching units, N being less than the total number of repeater sections of the system, and the length of the branching submarine optical fiber cable for connecting each branching unit is less than or equal to the length of the trunk submarine optical fiber cable of the repeater section, and the distance between two adjacent branching units is more than twice the length of the trunk submarine optical fiber cable of the repeater section, it is only necessary to add one uplink optical fiber to transmit the vibration monitoring signal for each branching submarine optical fiber cable by time division multiplexing, and when the length of the branching submarine optical fiber cable for connecting each branching unit is less than or equal to the length of the trunk submarine optical fiber cable of the repeater section, and the distance between two adjacent branching units is more than the length of the trunk submarine optical fiber cable of the repeater section and less than twice the length of the trunk submarine optical fiber cable of the repeater section, it is only necessary to add two uplink optical fibers to transmit the vibration monitoring signal for each branching submarine optical fiber cable by a combined method of space division multiplexing and time division multiplexing. Thus, the overlap of vibration monitoring signal pulses for the branching submarine optical fiber cables of two adjacent branching units will be avoided.

[0020] Compared with the prior art, the repeater submarine optical fiber cable vibration monitoring system based on time division and space division multiplexing according to the present invention has the following advantages: (i) it deals with the problem that the submarine optical fiber cable vibration monitoring system cannot pass through the repeaters of each section of the submarine optical fiber cable, and increases the detection distance of the submarine optical fiber cable vibration monitoring system from within 100 km to several thousand km, thereby meeting the real-time monitoring requirements of physical safety as required for long-distance submarine optical fiber cables; (ii) since the present monitoring system performs underwater optical signal transmission for the entire route, there is no need for a digital sampling module, and there is no need to increase the submarine active devices; (iii) the detection light source uses only one wavelength, thereby reducing the cost of the equipment; (iv) the downlink frequency modulated pulse signal occupies only one channel of the downlink optical fiber and can be wavelength division multiplexed with other digital communication service signals, while the uplink submarine cable monitoring signal is , which occupies only one channel of each of the n uplink optical fibers and can be wavelength division multiplexed together with other digital communication service signals; (v) it corresponds to vibration monitoring of a branch submarine optical fiber cable of a submarine optical fiber cable, and realizes both vibration monitoring of the trunk cable and vibration monitoring of its branch submarine optical fiber cable; (vi) the solution of the present invention based on OFDR technology can not only completely replace the COTDR device, but also realize real-time monitoring and location of vibration, and location of fault points of submarine cables, and the coherent integration time per unit time of the device is more than 1000 times that of the COTDR coherent integration time, and the sampling and signal processing of the coherent signal can be completed within a few seconds, therefore, compared with the response speed of COTDR of about 10 minutes, the response speed and response sensitivity of the device are greatly improved. [Brief description of the drawings]

[0021] [Figure 1] 1 is a schematic diagram showing the configuration of a repeater submarine optical fiber cable vibration monitoring system based on time division and space division multiplexing according to a first embodiment. [Diagram 2]1 is a schematic diagram showing the configuration of a narrow linewidth vibration monitoring pulse in the time domain of a repeater submarine optical fiber cable vibration monitoring system based on time division and space division multiplexing according to a first embodiment. FIG. [Diagram 3] 1 is a schematic diagram showing the configuration of an MZ optical fiber interferometer of a repeater submarine optical fiber cable vibration monitoring system based on time division and space division multiplexing according to a first embodiment. FIG. [Figure 4] FIG. 11 is a schematic diagram showing the configuration of a repeater submarine optical fiber cable vibration monitoring system based on time division and space division multiplexing according to a second embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] First embodiment of repeater submarine optical fiber cable vibration monitoring system based on time division and space division multiplexing FIG. 1 shows a schematic diagram of a repeater submarine optical fiber cable vibration monitoring system based on time division and space division multiplexing according to a first embodiment of the present invention. The detection optical signal output by the detection light source is input to the downlink transmission optical fiber of the submarine optical fiber cable. The downlink transmission optical fiber of each section is first connected to a downlink repeater amplifier, then to an optical fiber interferometer, and then to the downlink transmission optical fiber of the next section. In this embodiment, the length of the downlink transmission optical fiber between two adjacent downlink repeater amplifiers is 100 km, which is called a repeater section. The detection light source in this embodiment is a narrow linewidth frequency modulated pulse light source. The frequency modulated pulse width of the detection optical signal is twice the round trip delay time for the submarine optical fiber cable of one repeater section, and its frequency modulated pulse period exceeds the round trip delay time for the entire length of the repeater submarine optical fiber cable to be monitored.

[0023] In this embodiment, the uplink transmission optical fiber of each repeater section includes two uplink optical fibers involved in transmitting the vibration monitoring signal to each repeater section.

[0024] FIG. 1 shows a schematic diagram of the repeater section I and repeater section II in this embodiment. The detection light source outputs a detection optical signal, which is connected to a downlink repeater amplifier I (i.e., a downlink EDFAI) of the repeater section I, then to an optical fiber interferometer I, and then to a downlink transmission optical fiber of section I. The detection optical signal generates a backward Rayleigh scattering signal in the downlink transmission optical fiber of the repeater section I, and the backward Rayleigh scattering signal interferes with a local optical signal in the optical fiber interferometer I to generate a vibration monitoring signal for the submarine optical fiber cable of the repeater section I. The vibration monitoring signal output by the optical fiber interferometer I is input to a filter I of the repeater section I. The filter I transmits the vibration monitoring signal for the submarine optical fiber cable of section I. The vibration monitoring signal passes through the optical fiber coupler I of this repeater section I and enters the uplink EDFAIa of the uplink optical fiber a of the uplink transmission optical fiber I, then passes through the uplink optical fiber a and is returned to the sampling channel of the sampling device, and is finally digitally sampled and output to the demodulation device. The configuration of the optical fiber interferometer II of the repeater section II is similar to that of the optical fiber interferometer I of the repeater section I. The vibration monitoring signal output by the optical fiber interferometer II is input to the filter II of the repeater section II. The vibration monitoring signal transmitted by the filter II passes through the optical fiber coupler II of the repeater section II and enters the uplink EDFA IIb of the uplink optical fiber IIb, and is returned from the uplink optical fiber b to the sampling channel b of the sampling device, and is finally digitally sampled and output to the demodulator. One uplink transmission optical fiber a transmits vibration monitoring signals for repeater sections I, III, V, VII, etc., and the other uplink optical fiber b transmits vibration monitoring signals for repeater sections II, IV, VI, VIII, etc. Depending on the difference in the uplink optical fiber and the signal pulse rising edge time, the demodulator distinguishes the vibration monitoring signals for different repeater sections. Figure 2 shows a schematic diagram of the configuration in the time domain of the vibration monitoring signal pulses transmitted by the two uplink optical fibers in this embodiment.

[0025] In this embodiment, the vibration monitoring signals for repeater sections I, III, V, VII, etc. are coupled to uplink optical fiber a, and the vibration monitoring signals for repeater sections II, IV, VI, VIII, etc. are coupled to uplink optical fiber b.

[0026] In this embodiment, the pulse width of the detection optical signal is slightly less than twice the round trip delay time for the undersea optical fiber cable in the repeater section, ie, 2 ms to 0.5 μs.

[0027] In this embodiment, as shown in FIG. 3, the optical fiber interferometer is an MZ interferometer, and includes an optical fiber splitter having a branching ratio of 90:10, an optical fiber circulator, and a 3 dB optical fiber coupler. In the optical fiber splitter, the detection optical signal is branched into two paths. One detection optical signal having a large branching ratio is input to the first port (1) of the optical fiber circulator, then output from the second port (2) of the optical fiber circulator, and then input to the downlink transmission optical fiber to continue the downlink transmission, and the other detection optical signal having a small branching ratio is input to the 3 dB optical fiber coupler as a local optical signal. The backward Rayleigh signal generated in the downlink transmission optical fiber is returned from the second port (2) of the optical fiber circulator to the optical fiber circulator, and input to the 3 dB optical fiber coupler through the third port (3) of the optical fiber circulator. In the 3 dB optical fiber coupler, the backward Rayleigh signal interferes with the local optical signal. The 3 dB optical fiber coupler outputs a submarine optical fiber cable vibration monitoring signal for the downlink transmission optical fiber of this repeater section.

[0028] In the MZ fiber optic interferometer of this embodiment, in the interference arm for the local oscillator light from the fiber optic splitter to the 3 dB fiber optic coupler, the fiber optic splitter is connected to a depolarizer before being connected to the 3 dB fiber optic coupler, and in the interference arm for the backward Rayleigh scattering signal from the fiber optic circulator to the 3 dB fiber optic coupler, the fiber optic circulator is connected to a depolarizer before being connected to the 3 dB fiber optic coupler. In this example, a Lyot depolarizer is used.

[0029] Second embodiment of repeater submarine optical fiber cable vibration monitoring system based on time division and space division multiplexing The basic configuration of the system is similar to that of the first embodiment, but a vibration monitoring branching section for the branch submarine optical fiber cables connected to the branching device is added. FIG. 4 shows a schematic configuration diagram of a relay section in which a trunk submarine optical fiber cable is connected to a specific branching device. In this embodiment, the trunk submarine optical fiber cable is connected to five branching devices. When the length of the branch submarine optical fiber cables connected to each branching device is equal to or less than the length of the trunk submarine optical fiber cable of the relay section, and the distance between two adjacent branching devices is more than twice the length of the trunk submarine optical fiber cable of the relay section, it is only necessary to add one uplink optical fiber c and transmit vibration monitoring signals for the five branch submarine optical fiber cables by time division multiplexing. In FIG. 4, the relay section is connected to one branch submarine optical fiber cable through one branching device. In the 1×2 optical fiber splitter, the detection optical signal is branched into two paths. In one path, the detection optical signal continues to be transmitted downlink along the downlink transmission optical fiber of the trunk submarine optical fiber cable, and in the other path, the detection optical signal is input to the branch cable optical fiber interferometer, the detection optical signal passes through the branch cable optical fiber interferometer, and then is continuously transmitted downlink along the branch submarine optical fiber cable, and the back Rayleigh scattering signal generated in the branch submarine optical fiber cable interferes with the local optical signal in the branch submarine cable optical fiber interferometer, and a vibration monitoring signal for the branch submarine optical fiber cable of this repeater section is obtained. The vibration monitoring signal for the branch submarine optical fiber cable is input to the branch cable optical fiber coupler via the branch cable filter, and then combined with a signal from the uplink optical fiber c that transmits the vibration monitoring signal for the branch submarine optical fiber cable in the uplink transmission optical fiber, and then transmitted uplink to the sampling channel c of the sampling device of the branch submarine optical fiber cable, and finally sent to the demodulation device after sampling.

[0030] When a trunk submarine optical fiber cable is connected to five branching devices, under the condition that the length of the branching submarine optical fiber cable connecting each branching device is equal to or less than the length of the trunk submarine optical fiber cable of the repeater section, and the distance between two adjacent branching devices is greater than the length of the trunk submarine optical fiber cable of the repeater section and less than twice the length of the trunk submarine optical fiber cable of the repeater section, it is only necessary to add two uplink optical fibers, i.e., uplink optical fiber c and uplink optical fiber d, and transmit the vibration monitoring signals for the five branching submarine optical fiber cables by a combined method of space division multiplexing and time division multiplexing, thereby ensuring that the vibration monitoring signal pulses for two adjacent branching devices do not overlap.

[0031] The above-mentioned embodiments are merely specific examples for further illustrating the objectives, technical solutions and beneficial effects of the present invention, and the present invention is not limited thereto. Any modifications, equivalent replacements, improvements, etc. made within the scope of the disclosure of the present invention are included in the protection scope of the present invention.

Claims

1. A repeater submarine optical fiber cable vibration monitoring system based on time division and space division multiplexing, monitoring vibration of a repeater submarine optical fiber cable, comprising: a detection light source, a repeater amplifier, a downlink transmission optical fiber, an optical fiber interferometer, an uplink transmission optical fiber, and a demodulator; the detection light source outputs a detection optical signal and is connected to the downlink transmission optical fiber of the repeater submarine optical fiber cable; the optical fiber length between two adjacent downlink repeater amplifiers is 100 km or less, which is called a repeater section; in the downlink transmission optical fiber of each repeater section, first the downlink repeater amplifier is connected, then the optical fiber interferometer is connected, and then the downlink transmission optical fiber of this section is connected; Each repeating section further includes a filter and an optical fiber coupler, the transmission wavelength of the filter being consistent with the center wavelength of the detection optical signal; the detection light source is a narrow-linewidth frequency-modulated pulse light source, the frequency-modulated pulse width of the detection light signal is n times the round-trip delay time of one repeater section for the repeater submarine optical fiber cable, n being an integer ranging from 2 to 8, and the frequency-modulated pulse period is greater than the round-trip delay time for the entire length of the repeater submarine optical fiber cable; The uplink transmission optical fiber of each repeater section includes at least n uplink optical fibers, the detection optical signal output by the detection light source is branched into two beams after entering the optical fiber interferometer of a particular repeater section, one beam is transmitted downlink along the downlink transmission optical fiber of this section, and the other beam is used as a local optical signal, the backward Rayleigh scattering signal generated in the downlink transmission optical fiber of this repeater section interferes with the local optical signal in the optical fiber interferometer to generate a vibration monitoring signal for the repeater submarine optical fiber cable of this repeater section, the vibration monitoring signal output by the optical fiber interferometer of this repeater section is input to the filter of this repeater section, and the filter transmits only the vibration monitoring signal, the output end of the filter is input to one of the uplink transmission optical fibers through the optical fiber coupler of this repeater section, and then to the uplink transmission optical fiber. the vibration monitoring signals of the n consecutive repeater sections are returned in sequence through the first to nth uplink transmission optical fibers, and the vibration monitoring signals of the next n consecutive repeater sections are also returned in sequence through the first to nth uplink optical fibers; the vibration monitoring signals for each repeater section returned through the uplink transmission optical fibers are respectively digitally sampled through the n sampling channels of the uplink sampling device, and then transmitted to a demodulation device; the sampling device includes an opto-electrical conversion module and an analog-digital conversion module; in the sampling device, the optical signal is converted into an electrical signal through opto-electrical conversion, and then into a digital signal through analog-digital conversion; the demodulation device distinguishes the vibration monitoring signals for each repeater section, analyzes and demodulates the data, and provides an early warning of the safety status of the repeater submarine optical fiber cable of each repeater section; a filter in a first to n-th repeater section transmits the resulting vibration monitoring signal to each section, the filter in one section is connected to a 1×2 optical fiber coupler in this section, and the 1×2 optical fiber coupler in an X-th repeater section is connected to a Y-th uplink optical fiber for beam combining, and Y=X mod n, that is, Y is the remainder obtained by dividing X by n, Y≠0, and if X is divisible by n, then Y=n.

2. n=2, a frequency-modulated pulse width of the detected optical signal is twice the round trip delay time for the repeater submarine optical fiber cable of one repeater section, the uplink transmission optical fiber includes at least two uplink optical fibers, the filter of one repeater section is connected to a 1×2 optical fiber coupler of this repeater section, and the 1×2 optical fiber coupler is connected to an uplink optical fiber connected to a filter of a repeater section that is one repeater section away from this repeater section for beam combining.

2. A repeater submarine optical fiber cable vibration monitoring system based on time division and space division multiplexing as claimed in claim 1.

3. The pulse width of the detection light source is less than n times the round trip delay time for one repeater section, and the difference between the pulse width and n times one round trip delay time for the repeater section ranges from 20 nanoseconds to 1 microsecond.

2. A repeater submarine optical fiber cable vibration monitoring system based on time division and space division multiplexing as claimed in claim 1.

4. the downlink repeater amplifier, the optical fiber interferometer, the filter, the optical fiber coupler, and the uplink repeater amplifier, as well as the detection light source, the sampling device, and the demodulation device in the first repeater section, are local devices disposed on land; 4. A repeater submarine optical fiber cable vibration monitoring system based on time division and space division multiplexing according to claim 1.

5. the optical fiber interferometer is an MZ optical fiber interferometer, and comprises an optical fiber splitter having a branching ratio of (5 / 95) to (50 / 50), an optical fiber circulator, and a 3 dB optical fiber coupler; in the optical fiber splitter, the detection optical signal is branched into two paths, the detection optical signal having a large branching ratio is input to a first port of the optical fiber circulator, then output from a second port of the optical fiber circulator, and then input to the downlink transmission optical fiber to continue downlink transmission, the detection optical signal having a small branching ratio is input to the 3 dB optical fiber coupler as a local optical signal, the backward Rayleigh scattering signal generated in the downlink transmission optical fiber is returned to the optical fiber circulator through the second port of the optical fiber circulator, then input to the 3 dB optical fiber coupler through a third port of the optical fiber circulator to interfere with the local optical signal, and the 3 dB optical fiber coupler outputs the vibration monitoring signal for the downlink transmission optical fiber of this relay section.

4. A repeater submarine optical fiber cable vibration monitoring system based on time division and space division multiplexing according to claim 1.

6. In the MZ optical fiber interferometer, an interference arm for a local oscillator light from the optical fiber splitter toward the 3 dB optical fiber coupler is connected to a depolarizer before being connected to the 3 dB optical fiber coupler, and an interference arm for a backward Rayleigh scattering signal from the optical fiber circulator toward the 3 dB optical fiber coupler is connected to a depolarizer before being connected to the 3 dB optical fiber coupler.

6. A repeater submarine optical fiber cable vibration monitoring system based on time division and space division multiplexing as claimed in claim 5.

7. The relay submarine optical fiber cable vibration monitoring system is added with a vibration monitoring branch for a branch submarine optical fiber cable, and the trunk submarine optical fiber cable of a specific relay section is connected to the branch submarine optical fiber cable, and accordingly, the uplink transmission optical fiber is added with one or two uplink optical fibers for transmitting a vibration monitoring signal to the branch submarine optical fiber cable, and in the 1×2 optical fiber splitter for the downlink transmission optical fiber, the detection optical signal is split into two paths, in one path, the detection optical signal continues downlink transmission along the downlink transmission optical fiber and enters the optical fiber interferometer of this relay section, and in the other path, the detection optical signal is split into a branch submarine cable optical fiber interferometer. a backscattered signal generated in the branch submarine optical fiber cable interferes with the local optical signal in the branch submarine optical fiber interferometer to obtain the vibration monitoring signal for the branch submarine optical fiber cable; the vibration monitoring signal for the branch submarine optical fiber cable is transmitted and filtered via a branch cable filter, and then input to an uplink optical fiber for transmitting the vibration monitoring signal for the branch submarine optical fiber cable through a 1×2 optical fiber coupler of the trunk submarine optical fiber cable, and then transmitted by an uplink to the sampling device located on land, and then input to the demodulation device.

4. A repeater submarine optical fiber cable vibration monitoring system based on time division and space division multiplexing according to claim 1.

8. said trunk submarine optical fiber cable is connected to N branching devices, N being less than the total number of relay sections of said relay submarine optical fiber cable vibration monitoring system; when the length of the branching submarine optical fiber cables for connecting each branching device is less than the length of the trunk submarine optical fiber cable of said relay section, and the distance between two adjacent branching devices is more than twice the length of the trunk submarine optical fiber cable of said relay section, it is only necessary to add one uplink optical fiber and transmit said vibration monitoring signal for each branching submarine optical fiber cable by a time division multiplexing method; when the length of the branching submarine optical fiber cables for connecting each branching device is less than the length of the trunk submarine optical fiber cable of said relay section, and the distance between two adjacent branching devices is more than the length of the trunk submarine optical fiber cable of said relay section, and less than twice the length of the trunk submarine optical fiber cable of said relay section, it is only necessary to add two uplink optical fibers and transmit said vibration monitoring signal for each branching submarine optical fiber cable by a combined method of space division multiplexing and time division multiplexing.

8. A repeater submarine optical fiber cable vibration monitoring system based on time division and space division multiplexing according to claim 7.

Images