CN110166117B - Fault monitoring system and method for long-distance double-path optical fiber unidirectional transmission - Google Patents
Fault monitoring system and method for long-distance double-path optical fiber unidirectional transmission Download PDFInfo
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- CN110166117B CN110166117B CN201910412705.7A CN201910412705A CN110166117B CN 110166117 B CN110166117 B CN 110166117B CN 201910412705 A CN201910412705 A CN 201910412705A CN 110166117 B CN110166117 B CN 110166117B
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
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- H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
- H04B10/07—Arrangements for monitoring or testing transmission systems; Arrangements for fault measurement of transmission systems
- H04B10/075—Arrangements for monitoring or testing transmission systems; Arrangements for fault measurement of transmission systems using an in-service signal
- H04B10/079—Arrangements for monitoring or testing transmission systems; Arrangements for fault measurement of transmission systems using an in-service signal using measurements of the data signal
- H04B10/0791—Fault location on the transmission path
Abstract
The invention discloses a fault monitoring system for long-distance two-way optical fiber unidirectional transmission, which comprises: the system comprises a laser, an optical coupler, a fault monitoring end and a long-distance multi-fiber optical cable module containing a fault point; the long-distance multi-fiber optical cable module comprises a long-distance multi-fiber optical cable, the long-distance multi-fiber optical cable comprises N optical fibers, N is more than or equal to 2, and the laser is connected with the input end of the optical coupler; at a head end of the long-haul multi-fiber cable, a first output end of the optical coupler is connected with one end of a first optical fiber in the long-haul multi-fiber cable; at the tail end of the long-distance multi-fiber optical cable, the other end of the first optical fiber is connected with the other end of the second optical fiber; at the head end of the long-distance multi-fiber optical cable, in DSP processing, high-precision multipoint vibration positioning of faults in the optical cable can be obtained according to the time difference of two-time phase modulation of the detection light, and multi-parameter transient changes including amplitude, phase and polarization can be recovered according to the received signals.
Description
Technical Field
The invention relates to the technical field of optical fiber fault monitoring, in particular to a fault monitoring system and method for long-distance double-path optical fiber unidirectional transmission.
Background
In an optical fiber communication transmission network comprising a long-distance buried optical cable, a submarine optical cable and a suspended optical cable, abnormal conditions often occur, such as sudden events of artificial excavation and damage at the periphery, natural disasters of earthquake typhoons or internal abnormity and the like. Therefore, there is a need for real-time monitoring of optical cables in such fiber optic communications transmission networks. However, to date, a failure prediction mechanism or an effective scheme for active monitoring of a multi-span long-distance optical fiber link compatible with an optical communication network is still lacking, and it is difficult to monitor an abnormal condition of a long-distance optical cable in real time. In addition, in order to maintain high reliability, the existing optical communication system needs to adopt a very conservative deployment strategy on network hardware, and a very large performance boundary is left on a communication link, for example, a system with a large bandwidth only occupies a small part of bandwidth resources, thereby causing high redundancy. Some existing fault detection technologies mostly adopt an Optical Time Domain Reflectometer (OTDR) technology based on backward rayleigh scattering and a sensing technology based on a double-arm mach-zehnder interferometer, but both of them have respective defects and cannot be well applied to commercial communication optical cables.
Specifically, the OTDR technique is insufficient: the technology utilizes backscattering generated by high-power optical pulses in optical fibers to detect the fault condition in the optical fibers, and has the biggest defect that the incidence of the high-power pulses can generate a nonlinear effect in the optical fibers, namely, the spectrum wavelength of the backscattering can be changed to cause that a system cannot work normally, and the monitoring distance of the system is in direct proportion to the power of the pulse light, so that the OTDR technology is quite difficult to apply to an optical fiber link of over one hundred kilometers; in addition, high power optical pulses in OTDR technology are likely to damage expensive equipment devices in the communication network topology.
The technical defects of the double-arm interferometer are as follows: according to the technology, beat frequency is carried out on a receiving end by utilizing transmission signals with two arms of an interferometer in unequal lengths to obtain fault signals on optical fibers, but because of the unequal lengths, two optical fibers cannot be located on the same optical cable and cannot generate the same polarization effect, the problem of polarization alignment is always a difficulty of a double-arm interference technology, and the technology is not enough because instantaneous change of polarization state parameters cannot be provided.
The existing other distributed optical fiber sensing schemes are difficult to realize long-distance optical fiber link monitoring compatible with an optical communication network because of the problems of coverage distance, signal to noise ratio and the like.
Therefore, there is a need in the industry to develop a method and system for monitoring a long-distance optical fiber link that is compatible with an optical communication network.
Disclosure of Invention
The invention aims to overcome the defects in the prior art and provides a fault monitoring system and method for long-distance two-way optical fiber unidirectional transmission.
The purpose of the invention is realized by the following technical scheme:
a fault monitoring system for long-distance two-way optical fiber unidirectional transmission comprises: the system comprises a laser, an optical coupler, a fault monitoring end and a long-distance multi-fiber optical cable module containing a fault point; the long-distance multi-fiber optical cable module comprises a long-distance multi-fiber optical cable, the long-distance multi-fiber optical cable comprises N optical fibers, N is more than or equal to 2, and the laser is connected with the input end of the optical coupler; at a head end of the long-haul multi-fiber cable, a first output end of the optical coupler is connected with one end of a first optical fiber in the long-haul multi-fiber cable; at the tail end of the long-distance multi-fiber optical cable, the other end of the first optical fiber is connected with the other end of the second optical fiber; one end of the second optical fiber is connected with the fault monitoring end at the head end of the long-distance multi-fiber optical cable; and the second output end of the optical coupler is connected with the fault monitoring end.
Preferably, the long-haul multi-fiber cable module further comprises repeaters for optical signal amplification, the repeaters being disposed between the long-haul multi-fiber cables.
Preferably, the long-haul multi-fiber cable module includes two lengths of long-haul multi-fiber cable and a repeater disposed between the two lengths of long-haul multi-fiber cable.
Preferably, the method further comprises the following steps: a first multiplexer, a second multiplexer, a first demultiplexer and a second demultiplexer; the first output end of the optical coupler is connected with the input end of the first multiplexer, and the output end of the first multiplexer is connected with one end of a first optical fiber in the long-distance multi-fiber optical cable; the other end of the first optical fiber is connected with the input end of a first demultiplexer, the output end of the first demultiplexer is connected with the input end of a second multiplexer, and the output end of the second multiplexer is connected with the other end of the second optical fiber; one end of the second optical fiber is connected with the input end of the second demultiplexer, and the output end of the second demultiplexer is connected with the fault monitoring end.
Preferably, the fault monitoring terminal includes: the 90-degree frequency mixer, the balance detector, the oscillator and the signal acquisition card are connected in sequence; the number of the balance detectors is 4, the 4 balance detectors are arranged side by side, and the input end of the 90-degree frequency mixer is connected with one end of the second optical fiber and the second output end of the optical coupler; or the fault monitoring end comprises: the 3dB coupler, the balance detector, the oscillator, the 90-degree mixer and the signal acquisition card are sequentially connected, and the input end of the 3dB coupler is connected with one end of the second optical fiber and the second output end of the optical coupler; or the fault monitoring end comprises: the input end of the photoelectric detector is connected with one end of the second optical fiber and the second output end of the optical coupler.
The fault monitoring method for the long-distance double-path optical fiber unidirectional transmission comprises the following steps:
s1, the laser generates continuous laser and splits the laser through the optical coupler, one path of the laser is used as probe light to enter a first optical fiber in the long-distance multi-fiber optical cable, and the other path of the laser is used as local oscillation light to be input to a fault monitoring end;
s2, transmitting the detection light in the first optical fiber, and modulating the phase of the detection light for the first time when the detection light passes through a fault point on the long-distance multi-fiber optical cable;
s3, the detection light is transmitted back to the second optical fiber in the long-distance multi-fiber optical cable for transmission, when the detection light passes through a fault point on the long-distance multi-fiber optical cable, the phase of the detection light is modulated for the second time, and the detection light with the phase modulated for the second time enters a fault monitoring end;
and S4, the fault monitoring end processes the local oscillation light and the detection light of which the phase is modulated for the second time, and the position of the fault point is obtained.
Preferably, step S1 includes: the laser generates continuous laser and is shunted by the optical coupler, one path of the continuous laser is used as detection light and enters a first optical fiber in the long-distance multi-fiber optical cable through the first multiplexer, and the other path of the continuous laser is used as local oscillation light and is input to the fault monitoring end.
Preferably, step S2 includes: the detection light is transmitted in the first optical fiber, and the phase of the detection light is modulated for the first time when the detection light passes through a fault point on the long-distance multi-fiber optical cable; the probe light is optically amplified while passing through the relay.
Preferably, step S3 includes: when the detection light is transmitted to the other end of the first optical fiber, the detection light passes through the first demultiplexer and the second multiplexer and then is transmitted back to the second optical fiber in the long-distance multi-fiber optical cable, and when the detection light passes through the repeater, the detection light is amplified again; and when the optical fiber passes through a fault point on the long-distance multi-fiber optical cable, the phase of the detection light is modulated for the second time, and the detection light with the second modulated phase enters a fault monitoring end through a second demultiplexer.
Preferably, step S4 includes: the detection light and the local oscillation light are converted into electric signals by a four-path balance detector after being mixed by a 90-degree mixer, and the electric signals are collected and processed by a signal collection card after passing through an oscillator; or step S4 includes: the detection light and the local oscillator light are subjected to beat frequency through a 3dB coupler and then converted into electric signals through a balance detector, the electric signals sequentially pass through an oscillator and a 90-degree frequency mixer, are collected through a signal acquisition card and are subjected to phase processing in a digital domain; or step S4 includes: the detection light is converted into an electric signal through the photoelectric detector, and the electric signal is collected and processed by the signal collection card after passing through the oscillator.
Compared with the prior art, the invention has the following advantages:
according to the scheme, the fault monitoring system for long-distance two-way optical fiber unidirectional transmission enters the first optical fiber in the long-distance multi-fiber optical cable through the detection light output by the optical coupler, and the other path of the detection light is input to a fault monitoring end as local oscillation light; the detection light is transmitted in the first optical fiber, and the phase of the detection light is modulated for the first time when the detection light passes through a fault point on the long-distance multi-fiber optical cable; the detection light is transmitted back to a second optical fiber in the long-distance multi-fiber optical cable for transmission, when the detection light passes through a fault point on the long-distance multi-fiber optical cable, the phase of the detection light is modulated for the second time, and the detection light with the phase modulated for the second time enters a fault monitoring end; and the fault monitoring end processes the local oscillation light and the detection light of which the phase is modulated for the second time to obtain the position of a fault point. The fault monitoring end can be flexibly changed according to the modulation mode of the signal, and has the modes of homodyne coherent reception, heterodyne coherent reception, intensity reception and the like. In DSP processing, high-precision multipoint vibration positioning of faults in the optical cable can be obtained according to the time difference of two-time phase modulation of the detection light, and multi-parameter transient changes comprising amplitude, phase and polarization can be recovered according to the received signals. The fault monitoring system for long-distance two-way optical fiber unidirectional transmission can be applied to active monitoring of optical fiber links of a long-distance optical communication system, and fault monitoring of almost all optical fiber link infrastructures from submarine optical cables to land long distance, metropolitan area and access is achieved.
Drawings
Fig. 1 is a schematic structural diagram of a fault monitoring system for long-distance two-way optical fiber unidirectional transmission according to embodiment 1.
Fig. 2 is a schematic structural diagram of a fault monitoring system for long-distance two-way optical fiber unidirectional transmission according to embodiment 2.
Fig. 3(a) is a signal spectrum output from the first output terminal of the optical coupler of embodiment 2.
Fig. 3(b) is a signal spectrum output from the output terminal of the first demultiplexer of embodiment 2.
Fig. 3(c) is a signal spectrum output from the second output terminal of the optical coupler of embodiment 2.
Fig. 4 is a schematic structural view of a fault monitoring terminal of embodiment 2.
Fig. 5 is a schematic structural view of a fault monitoring terminal of embodiment 3.
Fig. 6 is a schematic structural view of a fault monitoring terminal of embodiment 4.
Fig. 7 is a schematic flow chart of a fault monitoring method for long-distance two-way optical fiber unidirectional transmission according to embodiment 1.
Detailed Description
The invention is further illustrated by the following figures and examples.
Example 1
Referring to fig. 1, a fault monitoring system for long-distance two-way optical fiber unidirectional transmission includes: the system comprises a laser, an optical coupler, a fault monitoring end and a long-distance multi-fiber optical cable module containing a fault point; the long-distance multi-fiber optical cable module comprises a long-distance multi-fiber optical cable, the long-distance multi-fiber optical cable comprises N optical fibers, N is more than or equal to 2, and the laser is connected with the input end of the optical coupler; at a head end of the long-haul multi-fiber cable, a first output end of the optical coupler is connected with one end of a first optical fiber in the long-haul multi-fiber cable; at the tail end of the long-distance multi-fiber optical cable, the other end of the first optical fiber is connected with the other end of the second optical fiber; one end of the second optical fiber is connected with the fault monitoring end at the head end of the long-distance multi-fiber optical cable; and the second output end of the optical coupler is connected with the fault monitoring end.
Referring to fig. 7, the method for monitoring the fault of the long-distance two-way optical fiber unidirectional transmission includes:
s1, the laser generates continuous laser and splits the laser through the optical coupler, one path of the laser is used as detection light and enters the first optical fiber in the long-distance multi-fiber optical cable after passing through the modulator, and the other path of the laser is used as local oscillation light and is input to the fault monitoring end;
s2, transmitting the detection light in the first optical fiber, and modulating the phase of the detection light for the first time when the detection light passes through a fault point on the long-distance multi-fiber optical cable; the detection light passes through a disturbance point or a fault point of the optical fiber in the transmission process of the optical fiber, and the phase of the detection light is correspondingly changed. The first optical fiber and the second optical fiber are any optical fibers in the long-distance multi-fiber optical cable.
S3, the detection light is transmitted back to the second optical fiber in the long-distance multi-fiber optical cable for transmission, when the detection light passes through a fault point on the long-distance multi-fiber optical cable, the phase of the detection light is modulated for the second time, and the detection light with the phase modulated for the second time enters a fault monitoring end; the scheme is that the fault is positioned and judged by utilizing the two-time phase change information of the detection light;
and S4, the fault monitoring end processes the local oscillation light and the detection light of which the phase is modulated for the second time, and the position of the fault point is obtained.
The detection light generates phase change of corresponding frequency under the vibration of different frequencies, and based on the phase change, the positions of corresponding vibration points under the vibration of different frequencies can be obtained by observing the time-frequency characteristics of the phase change of signals of the front transmission optical fiber (the first optical fiber) and the back transmission optical fiber (the second optical fiber); secondly, by observing a time domain/space domain two-dimensional image obtained by superposing sensing signals (detection light), different vibration points form a discontinuous singular point on the vibration position, and the vibration position is calibrated by the positions of the points.
Designing technical parameters: the embodiment uses a narrow linewidth laser with the width of 1khz or less at the transmission end during testing; the optical cable is a commercial multi-fiber optical cable; the used optical fiber is a common G.652 single-mode optical fiber; the long-distance multi-fiber optical cable module is a loop system formed by two paths of acousto-optic modulators.
The embodiment provides a fault monitoring system and a fault monitoring method for long-distance two-way optical fiber unidirectional transmission, a new optical fiber communication fault monitoring mechanism is developed through a forward transmission positioning technology of two-way optical fibers, the reliability of a communication system can be improved to a great extent, and a long-distance communication optical cable can better play a role.
Example 2
The present embodiment is different from embodiment 2 in that, referring to fig. 2, the long-distance multi-fiber cable module further includes a repeater 15 for optical signal amplification, and the repeater 15 is disposed between the long-distance multi-fiber cables. Specifically, the long-haul multi-fiber cable module includes two lengths of long-haul multi-fiber cable and a repeater 15, the repeater 15 being disposed between the two lengths of long-haul multi-fiber cable. More specifically, each long-distance multi-fiber optical cable is 80 km.
In this embodiment, the fault monitoring system for long-distance two-way optical fiber unidirectional transmission further includes: a first multiplexer 11, a second multiplexer 13, a first demultiplexer 12, and a second demultiplexer 14; the first output end of the optical coupler is connected with the input end of the first multiplexer 11, and the output end of the first multiplexer 11 is connected with one end of a first optical fiber in the long-distance multi-fiber optical cable; the other end of the first optical fiber is connected with the input end of a first demultiplexer 12, the output end of the first demultiplexer 12 is connected with the input end of a second multiplexer 13, and the output end of the second multiplexer 13 is connected with the other end of the second optical fiber; one end of the second optical fiber is connected to the input end of the second demultiplexer 14, and the output end of the second demultiplexer 14 is connected to the fault monitoring end. The spectrum of the signal output from the first output terminal of the optical coupler after passing through the modulator is shown in fig. 3 (a). The spectrum of the signal output at the output of the first demultiplexer is shown in fig. 3 (b). The spectrum of the signal output from the second output terminal of the optical coupler is shown in fig. 3 (c).
In this embodiment, the fault monitoring terminal includes: the device comprises a 90-degree frequency mixer (2 × 890-degree Hybrid), a balanced detector (BPD), an Oscillator (OSC) and a signal acquisition card (DSP) which are connected in sequence; the number of the balance detectors is 4, the 4 balance detectors are arranged side by side, and the input end of the 90-degree frequency mixer is connected with one end of the second optical fiber and the second output end of the optical coupler.
The fault monitoring method for the long-distance two-way optical fiber unidirectional transmission comprises the following steps:
the laser generates continuous laser and splits the laser through the optical coupler, one path of the laser is used as probe light and enters a first optical fiber in the long-distance multi-fiber optical cable through the first multiplexer 11, and the other path of the laser is used as local oscillation light (Lo) and is input to the fault monitoring end.
The detection light is transmitted in the first optical fiber, and the phase of the detection light is modulated for the first time when the detection light passes through a fault point on the long-distance multi-fiber optical cable; the probe light is optically amplified while passing through the relay 15.
When the detection light is transmitted to the other end of the first optical fiber, the detection light passes through the first demultiplexer 12 and the second multiplexer 13 and then is transmitted back to the second optical fiber in the long-distance multi-fiber optical cable, and when the detection light passes through the repeater 15, the detection light is amplified again; and when the optical fiber passes through a fault point on the long-distance multi-fiber optical cable, the phase of the detection light is modulated for the second time, and the detection light (Sig) with the second modulated phase enters a fault monitoring end through the second demultiplexer 14.
The detection light and the local oscillation light are converted into electric signals by a four-path balance detector after being mixed by a 90-degree mixer, and the electric signals are collected by a signal collection card (DSP) and processed by data after passing through an oscillator; the method is a homodyne coherent reception method. In the process, high-precision multipoint vibration positioning of faults in the optical cable is obtained according to the time difference of the two-time phase modulation of the detection light, and the electric signal can recover multi-parameter transient changes comprising amplitude, phase and polarization. The signal receiving end adopts two groups of same coherent receivers with the bandwidth exceeding 200 MHz.
Example 3
The difference between this embodiment and embodiment 2 is that the fault monitoring end includes: the optical fiber coupler comprises a 3dB coupler (3-dB coupler), a balanced detector (BPD), an Oscillator (OSC), a 90-degree mixer (Digital 90-degree Hybrid) and a signal acquisition card (DSP), wherein the 3dB coupler, the BPD coupler, the Oscillator (OSC), the 90-degree mixer and the signal acquisition card (DSP) are sequentially connected, and the input end of the 3dB coupler is connected with one end of a second optical fiber and the second output end of an optical coupler; step S4 includes: the detection light and the local oscillator light are subjected to beat frequency through a 3dB coupler and then converted into electric signals through a balance detector, the electric signals sequentially pass through an oscillator and a 90-degree frequency mixer, are collected through a signal acquisition card and are subjected to phase processing in a digital domain; the method is a heterodyne coherent reception method.
Example 4
The difference between this embodiment and embodiment 2 is that the fault monitoring end includes: and the input end of the photoelectric detector is connected with one end of the second optical fiber and the second output end of the optical coupler. The detection light is converted into an electric signal through the photoelectric detector, and the electric signal is collected and processed by the signal collection card after passing through the oscillator. This method is intensity reception.
The above-mentioned embodiments are preferred embodiments of the present invention, and the present invention is not limited thereto, and any other modifications or equivalent substitutions that do not depart from the technical spirit of the present invention are included in the scope of the present invention.
Claims (9)
1. A fault monitoring system for long-distance two-way optical fiber unidirectional transmission is characterized by comprising: the system comprises a laser, an optical coupler, a fault monitoring end and a long-distance multi-fiber optical cable module containing a fault point; the long-distance multi-fiber optical cable module comprises a long-distance multi-fiber optical cable, the long-distance multi-fiber optical cable comprises N optical fibers, N is more than or equal to 2, and the laser is connected with the input end of the optical coupler;
at a head end of the long-haul multi-fiber cable, a first output end of the optical coupler is connected with one end of a first optical fiber in the long-haul multi-fiber cable;
at the tail end of the long-distance multi-fiber optical cable, the other end of the first optical fiber is connected with the other end of the second optical fiber;
one end of the second optical fiber is connected with the fault monitoring end at the head end of the long-distance multi-fiber optical cable;
the second output end of the optical coupler is connected with the fault monitoring end;
the fault monitoring method for the long-distance double-path optical fiber unidirectional transmission comprises the following steps:
s1, the laser generates continuous laser and splits the laser through the optical coupler, one path of the laser is used as probe light to enter a first optical fiber in the long-distance multi-fiber optical cable, and the other path of the laser is used as local oscillation light to be input to a fault monitoring end;
s2, transmitting the detection light in the first optical fiber, and modulating the phase of the detection light for the first time when the detection light passes through a fault point on the long-distance multi-fiber optical cable;
s3, the detection light is transmitted back to the second optical fiber in the long-distance multi-fiber optical cable for transmission, when the detection light passes through a fault point on the long-distance multi-fiber optical cable, the phase of the detection light is modulated for the second time, and the detection light with the phase modulated for the second time enters a fault monitoring end;
and S4, the fault monitoring end processes the local oscillation light and the detection light of which the phase is modulated for the second time, and the position of the fault point is obtained.
2. The system of claim 1, wherein the long haul multi-fiber cable module further comprises repeaters for optical signal amplification, the repeaters being disposed between the long haul multi-fiber cables.
3. The system of claim 2, wherein the long-haul multi-fiber cable module comprises two lengths of long-haul multi-fiber cable and a repeater disposed between the two lengths of long-haul multi-fiber cable.
4. The system for fault monitoring of long haul two-way fiber optic uni-directional transmission of claim 1 further comprising: a first multiplexer, a second multiplexer, a first demultiplexer and a second demultiplexer;
the first output end of the optical coupler is connected with the input end of the first multiplexer, and the output end of the first multiplexer is connected with one end of a first optical fiber in the long-distance multi-fiber optical cable;
the other end of the first optical fiber is connected with the input end of a first demultiplexer, the output end of the first demultiplexer is connected with the input end of a second multiplexer, and the output end of the second multiplexer is connected with the other end of the second optical fiber;
one end of the second optical fiber is connected with the input end of the second demultiplexer, and the output end of the second demultiplexer is connected with the fault monitoring end.
5. The system for fault monitoring of long-distance two-way optical fiber unidirectional transmission according to claim 1, wherein the fault monitoring end comprises: the 90-degree frequency mixer, the balance detector, the oscillator and the signal acquisition card are connected in sequence; the number of the balance detectors is 4, the 4 balance detectors are arranged side by side, and the input end of the 90-degree frequency mixer is connected with one end of the second optical fiber and the second output end of the optical coupler; or
The fault monitoring end comprises: the 3dB coupler, the balance detector, the oscillator, the 90-degree mixer and the signal acquisition card are sequentially connected, and the input end of the 3dB coupler is connected with one end of the second optical fiber and the second output end of the optical coupler; or
The fault monitoring end comprises: the input end of the photoelectric detector is connected with one end of the second optical fiber and the second output end of the optical coupler.
6. The system for monitoring the fault of the long-distance two-way optical fiber unidirectional transmission according to claim 1, wherein the step S1 comprises:
the laser generates continuous laser and is shunted by the optical coupler, one path of the continuous laser is used as detection light and enters a first optical fiber in the long-distance multi-fiber optical cable through the first multiplexer, and the other path of the continuous laser is used as local oscillation light and is input to the fault monitoring end.
7. The system for monitoring the fault of the long-distance two-way optical fiber unidirectional transmission according to claim 1, wherein the step S2 comprises:
the detection light is transmitted in the first optical fiber, and the phase of the detection light is modulated for the first time when the detection light passes through a fault point on the long-distance multi-fiber optical cable; the probe light is optically amplified while passing through the relay.
8. The system for monitoring the fault of the long-distance two-way optical fiber unidirectional transmission according to claim 7, wherein the step S3 comprises:
when the detection light is transmitted to the other end of the first optical fiber, the detection light passes through the first demultiplexer and the second multiplexer and then is transmitted back to the second optical fiber in the long-distance multi-fiber optical cable, and when the detection light passes through the repeater, the detection light is amplified again; and when the optical fiber passes through a fault point on the long-distance multi-fiber optical cable, the phase of the detection light is modulated for the second time, and the detection light with the second modulated phase enters a fault monitoring end through a second demultiplexer.
9. The system for monitoring the fault of the long-distance two-way optical fiber unidirectional transmission according to claim 1, wherein the step S4 comprises: the detection light and the local oscillation light are converted into electric signals by a four-path balance detector after being mixed by a 90-degree mixer, and the electric signals are collected and processed by a signal collection card after passing through an oscillator; or
Step S4 includes: the detection light and the local oscillator light are subjected to beat frequency through a 3dB coupler and then converted into electric signals through a balance detector, the electric signals sequentially pass through an oscillator and a 90-degree frequency mixer, are collected through a signal acquisition card and are subjected to phase processing in a digital domain; or
Step S4 includes: the detection light is converted into an electric signal through the photoelectric detector, and the electric signal is collected and processed by the signal collection card after passing through the oscillator.
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