Disturbance detection using spatial resolution with a track monitoring system

Abstract

To provide spatially resolved disturbance detection using a line monitoring system.SOLUTION: The line monitoring system may include: a laser source to launch a plurality of pulsed probe signals; and an optical transmission system, comprising a plurality of loopbacks, to receive the plurality of pulsed probe signals, and direct the plurality of pulsed probe signals through the plurality of loopbacks. The system may include a receiver to receive a plurality of return signals, derived from the plurality of pulsed probe signals, from the transmission system, and a disturbance detection system coupled to the receiver and used to measure a phase difference between a polarization of a pair of return signals of the plurality of return signals. The pair of return signals may be received from a pair of loopbacks of the plurality of loopbacks, a first loopback, and a second return signal from a second loopback. The disturbance detection system may determine a location of a disturbance, based upon the phase difference.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure generally relates to the field of submarine communications, and more specifically, to techniques for measuring disturbances using line monitoring equipment.

Background Art

[0002] Optical fiber cables are connected to distant continents along the seabed, and most international traffic on the Internet propagates through these cables, which constitute the backbone of the transmission system. Generally, communication via optical fiber cables is performed using optical pulses, which may be distorted during a transmission period of thousands of kilometers across the sea. In addition to transmitting communication information, the transmission system may be configured to provide information regarding cable quality using so-called line monitoring equipment. The line monitoring equipment can transmit a probe signal and detect a feedback signal, which provides information regarding an abnormality in the optical fiber cable within the transmission system, for example. Recently, it has been proposed that disturbances outside the optical fiber (such as an earthquake) can be detected by monitoring changes in an optical signal (such as the state of polarization (SOP) within the optical fiber). Recently, there has been a report of detecting a change in the SOP of a submarine optical fiber cable in response to an earthquake located 1000 kilometers away from the optical fiber cable. However, there is a lack of a system and technique capable of detecting a disturbance whose position is accurately spatially resolved outside the transmission system.

[0003] The present disclosure is provided in view of these and other considerations.

Summary of the Invention

Problems to be Solved by the Invention

[0004] The present invention provides a simplified explanation of the refined concepts that will be further described in the following detailed description. The present invention is not intended to identify important or necessary features of the subject matter for which protection is sought, nor is it intended to help determine the scope of the subject matter for which protection is sought. [Means for solving the problem]

[0005] In the first embodiment, a line monitoring system is provided. The line monitoring system may include a laser light source for transmitting a plurality of pulse probe signals, and an optical transmission system including a plurality of loopbacks, configured to receive the plurality of pulse probe signals and guide the plurality of pulse probe signals to pass through the plurality of loopbacks. The system may also include a receiver for receiving a plurality of feedback signals derived from the plurality of pulse probe signals from the optical transmission system, and a disturbance detection system used to measure the phase difference between the polarizations of the feedback signal pairs of the plurality of feedback signals, and coupled to the receiver. The feedback signal pairs can be received from a loopback pair of the plurality of loopbacks, a first loopback, and a second loopback. The disturbance detection system can also determine the location of disturbances based on the phase difference.

[0006] In another embodiment, a method for positioning disturbances using a transmission system is provided. The method may include transmitting a probe beam containing a plurality of pulsed probe signals from a laser probe source. The method may also include detecting a plurality of feedback signals received from a plurality of loopbacks provided along the optical transmission system, derived from the plurality of pulsed probe signals. The method may also include measuring the phase difference between the polarizations of feedback signal pairs of the plurality of feedback signals and determining the location of disturbances outside the optical transmission system based on the phase difference. Here, the feedback signal pairs are received from a loopback pair of the plurality of loopbacks, a first loopback, and a second loopback.

[0007] In further embodiments, the line monitoring system may include a laser light source for transmitting a plurality of pulse probe signals, a polarization rotation device configured to rotate the polarization of the plurality of pulse probe signals, and an optical transmission system including a plurality of loopbacks, configured to receive the plurality of pulse probe signals and to guide the plurality of pulse probe signals to pass through the plurality of loopbacks. The line monitoring system may also include a receiver for receiving a plurality of feedback signals derived from the plurality of pulse probe signals from the optical transmission system, and a disturbance monitoring system coupled to the receiver. The disturbance monitoring system may be configured to measure the phase difference between the polarizations of feedback signal pairs of the plurality of feedback signals, the feedback signal pairs being received from a loopback pair of the plurality of loopbacks, a first loopback, and a second loopback. [Brief explanation of the drawing]

[0008] [Figure 1] A schematic diagram of an exemplary embodiment of a line monitoring system for testing optical fibers according to this disclosure is shown. [Figure 2] The details of the LME system according to the embodiments of this disclosure are shown below. [Figure 3A] One embodiment of the polarization rotation device 108 according to the embodiments of the present disclosure is shown. [Figure 3B] This shows the electric field output at X and Y for one period of a sine function operating at 1 GHz. [Figure 3C] This shows the motion of the Stokes vector generated by a polarization rotation device in both ideal and practical cases. [Figure 4A] The principle of polarization decoding by modulation phase detection according to an embodiment of this disclosure is shown. [Figure 4B] The principle of polarization decoding by modulation phase detection according to an embodiment of this disclosure is shown. [Figure 4C] The principle of polarization decoding by modulation phase detection according to an embodiment of this disclosure is shown. [Figure 5A]The components for determining the disturbance location using the LME system according to each embodiment of this disclosure are shown. [Figure 5B] An embodiment of the disturbance location is shown, where a Fourier analysis is performed and the input is as shown. [Figure 6] The geometric shape of a special application example is shown, where the axis of disturbance is aligned with or close to the detector vector S1. [Figure 7] The geometric shape of another special application example is shown, where the detectors are aligned along S3. [Figure 8] An exemplary process flow is shown. [Modes for carrying out the invention]

[0009] This embodiment contributes to detecting disturbances (including submarine earthquakes) and determining position using a Line Monitoring Equipment (LME) for a submarine communication system. In each embodiment, multiple feedback signals are generated using a loopback system associated with the line monitoring equipment, and these feedback signals are used to determine positional information related to the disturbance. The LME transmitter can generate a signal with a specific polarization, where the receiver can determine the disturbance by measuring the phase of the returned polarization rotation.

[0010] Each embodiment provides a line monitoring system, primarily shown in Figure 1. The line monitoring system 100 in Figure 1 generates signals transmitted via an optical transmission system (shown as a submarine system 110) using a transmitter 102. The submarine system 110 may include, for example, a plurality of spaced loopbacks along the seabed. The line monitoring system 100 further comprises a receiver 112 configured to receive a plurality of feedback signals obtained from the signals transmitted by the transmitter 102.

[0011] In each embodiment, the transmitter 102 comprises a laser light source 104, a modulator 106, and a polarization rotation device 108. The laser light source 104 can generate a probe beam composed of multiple pulse probe signals, as shown, for example, in the probe beam 105.

[0012] According to each embodiment of the present disclosure, the modulator 106 can broaden the bandwidth of the pulse probe signal to a suitable bandwidth, for example, within the range of 25 MHz, e.g., 10 MHz, 25 MHz, 50 MHz, 100 MHz, or a similar bandwidth value according to each non-limiting embodiment. Considerations for selecting the target bandwidth include the minimum value of the electrical filter for detecting the feedback signal.

[0013] The polarization rotation device 108 is installed between the laser light source 104 and the submarine system 110 and is provided to rotate the polarization of multiple pulse probe signals generated by the laser light source 104 at a specific rotation frequency. In some non-limiting examples, the rotation frequency is in the range of 0.5 GHz to 5 GHz (e.g., 1 GHz).

[0014] In each embodiment, the pulse length of the pulsed probe signal generated by the laser light source 104 may be any suitable length. In a specific embodiment, the pulse length of the pulsed probe signal constituting the probe beam 105 may be shorter than the time delay between different loopback paths in the submarine system 110. Specifically, the pulsed probe signal of the probe beam 105 can be represented by pulse length, while the submarine system 110 is represented by the local differential propagation time as the probe signal is conducted and passes through adjacent loopbacks in the submarine system 110. In a particular embodiment, the pulse lengths of these probe signals may be set to be smaller than the local differential propagation time defined above. Also, according to some embodiments, the pulse frequency of the probe beam may be such that a given probe signal passes through all loopbacks in the transmission system and returns to the receiver before transmitting the next probe signal. In other words, the pulse period of the probe beam may be greater than the maximum propagation time, where the maximum propagation time is the duration for which the signal propagates from the laser light source to the receiver as it passes through the last loopback furthest from the laser light source. Therefore, each feedback signal of the first pulse probe signal is received by the receiver 112 before the laser light source 104 generates the second pulse probe signal immediately after the first pulse probe signal.

[0015] Turning to receiver 112, the receiver 112 may be configured as an optical heterodyne. The receiver 112 comprises a photodetector 116 and a feedback tap 114, configured to extract information (e.g., phase or frequency modulation of the feedback signal) from the feedback signal 115, where the feedback signal is compared with standard or reference light from a “local oscillator” (LO), and if the signal does not carry information, the local oscillator has a fixed offset in frequency and phase with respect to the signal.

[0016] The line monitoring system 100 further includes a phase measurement system 120. As described in detail below, the phase measurement system 120 may include various components (not shown individually) for monitoring the polarization phase difference between different feedback signals, and can determine the position of the disturbance based on the phase difference. More specifically, it can monitor the polarization phase difference between a pair of feedback signals received from the loopback pair of the submarine system 110.

[0017] As further shown in FIG. 1, the receiver 112 may include a feedback tap 114, where the feedback tap has a first input for receiving a feedback signal from the submarine system 110 and also has a second input for receiving a polarization signal. The feedback tap 114 is connected to the photodetector 116 via an output.

[0018] Figure 2 shows the details of the LME system 200 of the loopback of the undersea system 110. For simplicity, only the loopback that returns the pulse probe signal from the right side is shown. According to each embodiment, the undersea system 110 may also have loopbacks in the opposite direction, but these are not shown. In this example, the monitoring of the disturbance 202 is performed from the left side of the figure. In the illustration of Figure 2, the loopbacks are shown as loopbacks 118-A to 118-N, but according to each embodiment, the number of loopbacks can be set according to the size of the length of the undersea system 110. Therefore, when the length of the transmission system is thousands of kilometers and the interval between loopbacks is 100 kilometers, the number of loopbacks may be dozens. As described in detail below, the probe beam generated by the transmitter can pass through different loopbacks to generate a plurality of feedback signals, where the different feedback signals are received by the receiver and analyzed in a manner that establishes the position of the disturbance outside the undersea system 110. Specifically, in the case of the pulse probe signal propagating through each of the loopbacks 118-A to 118-N, the change in polarization phase can be measured. Such a change in polarization phase can be used to establish the polarization phase difference between the pulse probe signals guided to pass through adjacent loopbacks, whereby the probe change in the polarization phase difference between a predetermined set of loopbacks can be used for positioning the disturbance.

[0019] Figure 3A shows one embodiment of the polarization rotation device 108 according to an embodiment of the present disclosure. As shown in the figure, the signal transmitted from the laser light source is split and guided along two paths, where the C1 bias is applied to the upper branch and the V2 bias is applied to the lower branch. The phase of the upper branch is represented by sin(Ωt), and the phase of the lower branch is represented by sin(Ωt + π / 2), where in one embodiment, the value of Ω may be 1 GHz.

[0020] As shown in Figure 3A, the polX signal from the upper branch and the polY signal from the lower branch can be routed by the polarization maintaining combiner. Therefore, the polarization rotation device 108 can output a linearly polarized wave that rotates at the frequency Ω.

[0021] Figure 3B shows the electric field output in X and Y for one period of a sinusoidal function operating at 1 GHz. Typically, the pulse probe signal is defined by its polarization state and can be represented by a set of Stokes parameters S1, S2, S3, where these parameters are based on a Poincaré sphere.

number

[0022] Figure 3C shows the motion of the Stokes vector generated by the polarization rotation device 108, where, ideally, the polarization generated moves mainly around a circle on the Poincaré sphere, but in various practical cases (actually), the polarization is not located within the circle.

[0023] Figures 4A to 4C illustrate the principle of polarization decoding by modulation phase detection according to embodiments of this disclosure. According to each embodiment, for ease of interpretation, the polarization-sensitive detector used in the receiver 112 can detect received polarization aligned only along S1, as shown in Figure 4A. Further shown in Figure 4B, it can be assumed that a disturbance due to birefringence rotates the Poincaré sphere around an axis, and in this example, the axis shown by the thick dashed line is approximately aligned with S3. For example, the value of the rotation frequency may be 1 GHz. In Figure 4C, the detected intensity is shown as a function of time for two different cases. The sinusoidal change of intensity as a function of time is shown. These curves establish a phase difference φ compared to the clock, obtaining φ(t=t1), φ(t=t2), etc., and the result φt This can generate the following. In other embodiments, phase shifts can be detected at any rate even when the detector is not aligned along S3.

[0024] Figure 5A shows the components for determining disturbances using an LME system according to each embodiment of the present disclosure. The system comprises a receiver 520 (transmitter not shown, but refer to transmitter 102) and a submarine system 110 depicted as a series of loopbacks, these loopbacks may be located on repeaters and have characteristic spacings between loopbacks across the transmission system. For example, in two non-limiting embodiments, a suitable spacing between loopbacks may be 50 km or 100 km. As previously stated, depending on the location of the disturbance 202, the disturbance 202 has different effects on the polarization phase shifts detected between adjacent loopbacks. In the example of Figure 5A, five loopbacks 501-505 are shown, but the submarine system 110 may have more loopbacks depending on the length of the transmission system, for example, several dozen. Loopback 501 generates a phase difference φ1(t), the adjacent loopback shown as loopback 502 generates a phase difference φ2(t), and the next loopback shown as loopback 503 generates a phase difference φ3(t). The difference between φ1(t) and φ2(t) can be expressed by the corresponding phase difference Δφ1(t), and the difference between φ2(t) and φ3(t) can be expressed by Δφ2(t). Similarly, loopback 504 can be expressed by the phase difference φ4(t), and loopback 505 can be expressed by the phase difference φ5(t), where each consecutive pair is related to an increment delta such as Δφ3(t), Δφ4(t), etc.

[0025] If disturbance 202 is present between two specific loopbacks, the phase difference between the two loopbacks is affected. In other words, the phase difference between the loopbacks under discussion is altered. In the example in Figure 5A, Δφ2(t) is affected by disturbance 202, while other phase differences between other loopback pairs of the subsea system 110 (Δφ1(t), Δφ3(t), Δφ4(t), etc.) are not affected. This result can be interpreted in the following way: Before the scenario in Figure 5A, assume that there is no disturbance 202, and first measure the following phases φ1, φ2, φ3, φ4 and represent them as the values ​​1, 1, 1, 1, ... (assuming the additional loopback values ​​of the subsea system 110 are also 1). Then, the phase differences of the pairs that can be calculated as Δφ1=φ2-φ1, Δφ2=φ3-φ2, Δφ3=φ4-φ3 are 0, 0, 0, ... (the values ​​of the additional phase differences of the additional loopback pairs of the submarine system 110 are also 0). Also, if disturbance 202 exists, disturbance 202 has a value of 1 (for example) between loopback 502 and loopback 503. In this case, for loopbacks further from receiver 520 starting from loopback 503, all phases φ3, φ4, φ5, φ6 increase by a disturbance value of 1, which generates values ​​of 1, 1, 2, 2... for phases φ1, φ2, φ3, φ4 (the values ​​of the remaining phases in the further loopbacks are also 2). However, in the above scenario, the increase in the paired phase differences Δφ1, Δφ2, Δφ3 is 0, 1, 0... (the values ​​of the remaining paired phase differences between loopback pairs with a large number are also 0). In other words, all phases associated with loopbacks beyond φ3 were corrected by a value of 1, but only one pair of phase difference increases (Δφ2) were corrected. That is, the location of the corrected pair of phase differences (Δφ2) represents a location along the transmission system, where loopbacks further from receiver 520 represent corrected polarization phases, but loopbacks closer to receiver 520 do not represent polarization phases corrected in response to disturbances.

[0026] It should be noted that different types of disturbances may be expected to generate disturbances at different characteristic frequencies. In the case of earthquakes, the appropriate frequencies to monitor may be within the range of 1 Hz. In some embodiments, the exemplary range for monitoring earthquakes can cover the range of 0.1 Hz to 5 Hz. As shown in Figure 5B, in one embodiment, a Fourier analysis can be performed, where the output is, for example, a power spectrum, as shown in the figure. In other embodiments, other algorithms may be employed.

[0027] In the example in Figure 5B, the change in polarization phase difference can be represented as a change in intensity, which is color-coded (different shading) in the shown illustration. In Figure 5B, the horizontal axis represents the position along the optical transmission system, and its distance can be specified by the plane of the two repeaters or loopbacks closest to the disturbance. The vertical axis can represent time. In Figure 5B, a series of three time slices is shown, representing three different examples. The third axis represents the frequency of the disturbance being monitored. Thus, the presence of the disturbance is represented by a change in intensity at a given position and frequency along the transmission system, which is characteristic of the disturbance. In the example shown, the disturbance is detected toward the left, and its position can represent the positions of two loopbacks L1 and L2 of the transmission system that are relatively close to the detector. At a certain frequency, the disturbance is detected to be located forward, and its frequency can represent, for example, 1 Hz.

[0028] Therefore, a 1 Hz earthquake located between L1 and L2 will cause a change in polarization at the location between loopbacks L1 and L2, occurring at a frequency of 1 Hz. By periodically or continuously monitoring the Fourier transform output in this frequency range, earthquakes that generate disturbances at this frequency affecting the transmission system's cables can be detected and located near loopbacks L1 and L2.

[0029] The notation in Figure 5B is for illustrative purposes only, and according to each embodiment, disturbances can be determined by using an appropriate processing component 512 of the phase measurement system 120 (e.g., a digital signal processor or artificial intelligence system) to analyze the polarization phase change (detected by the receiver (e.g., receiver 112)) as a function of frequency, position along the transmission system, etc.

[0030] While the method described above is applicable to general disturbance cases, in some embodiments, the detection of polarization phase shifts can be modified to account for special cases.

[0031] Figure 6 shows an example where the disturbance axis aligns with or is close to the detector vector S1. In this example, another finφ i (f,N) may also be used.

[0032] In the special case shown in Figure 7, the detectors can be aligned along S3, where phase measurement does not function due to zero modulation amplitude. In this case, according to one embodiment, second-harmonic distortion can be used. In another embodiment, multiple polarizations can be detected. In yet another embodiment, AI (artificial intelligence) may be employed to extract information from other DL-PMPs.

[0033] Alternatively, in some embodiments, one or more receiver detectors can be used, each detector aligned along a different axis on a Poincaré sphere. In one example, for illustrative purposes, the first detector is aligned along S3 and the second detector along S2. The first detector aligned along S3 may not be able to detect the phase in the above case, but the S2 detector can easily measure the phase. In other words, if the circular trajectory rotates around S3, the projection onto S3 does not change, but the projection onto S2 does. Of course, in embodiments using two separate receiver detectors, a splitter (e.g., a 3dB splitter) is also needed to divide the returned optical signal into two paths, where each path includes a tap for mixing the local oscillator and the detector.

[0034] In another embodiment, the use of a fully coherent receiver capable of detecting the precise polarization state at any given time may be employed. In subsequent embodiments, the architecture becomes more complex, as will be understood by those skilled in the art.

[0035] Figure 8 shows an exemplary process flow diagram 800. In block 802, a probe beam is transmitted from a laser probe source. In some embodiments, the laser probe source may be a pulsed laser light source. According to each non-limiting embodiment, in some embodiments, the probe beam may be spread to an appropriate bandwidth such as 10 MHz, 25 MHz, 50 MHz, 100 MHz or similar values ​​according to each non-limiting embodiment.

[0036] In block 804, the probe beam is guided to pass through a polarization rotation device. The polarization rotation device can rotate multiple pulsed probe signals generated by the laser light source at a specific rotation frequency. In some non-limiting examples, the rotation frequency is in the range of 0.5 GHz to 5 GHz, for example, 1 GHz. According to some embodiments, the polarization rotation device can use known components (e.g., birefringent waveplates).

[0037] In block 806, a probe beam is transmitted through a transmission system, such as a long-range submarine optical communication system. Thus, the transmission system may include multiple loopbacks. In some examples, the loopbacks can be spaced regularly apart along the transmission system (e.g., tens of thousands of kilometers). Different loopbacks along the transmission system can create different paths between the transmitter (e.g., with a laser light source) and the receiver. Specifically, the characteristic of the different paths between different loopbacks is the differential propagation time for when the probe signal is conducted and passes through the path of an adjacent loopback. According to some embodiments, the pulse length of the probe beam may be set to be less than the differential propagation time. According to some embodiments, the pulse frequency of the probe beam may be such that a given probe signal passes through all the loopbacks of the transmission system and returns to the receiver before transmitting the next probe signal.

[0038] In block 808, the detector receives a feedback signal based on multiple pulse probe signals. In some embodiments, the detector may be a polarization-sensitive detector. In some examples, the detector can be oriented to receive polarization signals along the S1 axis of the Poincaré sphere.

[0039] Block 810 monitors the phase difference of the feedback signals between adjacent loopbacks in the transmission system. The phase difference can be monitored for all adjacent loopback pairs in the transmission system, or for fewer adjacent loopback pairs than all adjacent loopback pairs in the transmission system.

[0040] In block 812, the location of the disturbance is determined based on the phase difference monitored in block 810. In one example, Fourier analysis is performed on phase difference data selected within a suitable frequency range (e.g., on the order of 1 Hz), where, based on the Fourier analysis, the phase difference change is expressed as an intensity change as a function of position along the transmission system.

[0041] Any element or step described herein in the singular and beginning with the term "one" or "one" should be understood not to exclude multiple elements or steps unless an exclusion is expressly stated. Furthermore, any reference in this disclosure to "one embodiment" should not be construed as excluding the existence of additional embodiments combined with similarly described features.

[0042] While this disclosure has referenced several embodiments, various modifications, changes, and alterations to the embodiments described are possible, provided they do not deviate from the art and scope of this disclosure as limited by the appended claims. Therefore, this disclosure is not limited to the embodiments described and has the entire scope as defined by the language of the appended claims and their equivalents.

Claims

1. A laser light source for transmitting multiple pulse probe signals, An optical transmission system including multiple loopbacks, configured to receive the multiple pulse probe signals and to guide the multiple pulse probe signals to pass through the multiple loopbacks, A receiver for receiving multiple feedback signals derived from multiple pulse probe signals from the optical transmission system, The receiver is coupled to a disturbance detection system, The disturbance detection system is configured to measure the phase difference between the polarizations of the feedback signal pairs of the plurality of feedback signals and to determine the location of the disturbance based on the phase difference. The aforementioned feedback signal pair is received from the loopback pairs of the plurality of loopbacks. Track monitoring system.

2. The system further comprises a polarization rotation device provided between the laser light source and the optical transmission system for rotating the polarization of the plurality of pulse probe signals, The characteristic of each of the aforementioned multiple feedback signals is the phase of polarization rotation fed back from a predetermined loopback. The disturbance detection system is configured to determine the position by measuring the change in the value of the phase difference related to the polarization returned from the adjacent loopback of the loopback pair. The track monitoring system according to claim 1.

3. The receiver is equipped with a feedback tap, The feedback tap has a first input for receiving the plurality of feedback signals, a second input for receiving the polarization signal, and an output coupled to a photodetector. The track monitoring system according to claim 1.

4. The aforementioned optical transmission system includes local differential propagation time, The local differential propagation time includes the difference between a first duration during which the pulse probe signal propagates from the laser light source and returns to the receiver when it is conducted and passes through a first loopback, and a second duration during which the pulse probe signal propagates from the laser light source and returns to the receiver when it is conducted and passes through a second loopback adjacent to the first loopback. The laser light source is configured to generate multiple pulse probe signals with pulse lengths shorter than the local difference propagation time. The pulses of the aforementioned plurality of feedback signals do not overlap with each other in the receiver. The track monitoring system according to claim 1.

5. The characteristic of the aforementioned multiple pulse probe signals is the pulse period, The pulse period is greater than the maximum propagation time. The maximum propagation time includes the duration for which the pulse probe signal is conducted and passes through the last loopback furthest from the laser light source, and returns to the receiver. Before the laser light source generates the second pulse probe signal immediately following the first pulse probe signal, each feedback signal of the first pulse probe signal is received by the receiver. The track monitoring system according to claim 4.

6. The aforementioned multiple pulse probe signals are defined by their polarization state, The aforementioned receiver is sensitive to polarization. The track monitoring system according to claim 1.

7. The characteristic of the aforementioned disturbance is the disturbance frequency. The disturbance detection system includes logic for generating a power spectrum for the pulses of the plurality of feedback signals within a frequency range exceeding the disturbance frequency range, The aforementioned disturbance includes frequencies in the range of 0.1 Hz to 10 Hz. A track monitoring system according to any one of claims 1 to 6.

8. A method for positioning disturbances using a transmission system, Transmitting a probe beam containing multiple pulsed probe signals from a laser probe source, The receiver detects multiple feedback signals received from multiple loopbacks provided along the transmission system, which are derived from the multiple pulse probe signals. This includes measuring the phase difference between the polarizations of multiple feedback signal pairs and determining the location of external disturbances based on the phase difference, The aforementioned feedback signal pair is received from multiple loopback pairs. Disturbance positioning method.

9. Measuring the aforementioned phase difference means This includes monitoring the polarization phase difference between a plurality of feedback signal pairs derived from a plurality of adjacent loopback pairs of the transmission system, The disturbance positioning method according to claim 8.

10. Transmitting the probe beam includes guiding the probe beam to a polarization rotation device and rotating the probe beam at a predetermined frequency. The disturbance positioning method according to claim 8.

11. Monitoring the phase difference includes receiving the plurality of feedback signals in an optical heterodyne receiver. The aforementioned multiple pulse probe signals are defined by their polarization state, The polarization detector included in the aforementioned optical heterodyne receiver is polarization sensitive. The disturbance positioning method according to claim 9.

12. This includes generating the plurality of pulse probe signals with a predetermined pulse length, A feature of the transmission system is the differential propagation time of the pulse probe signals when the pulse probe signal is conducted and passes through loopbacks adjacent to the plurality of loopbacks, The predetermined pulse length is smaller than the differential propagation time. The disturbance positioning method according to claim 8.

13. The characteristic of the aforementioned multiple pulse probe signals is the pulse period, The method further includes setting the pulse period to be greater than the maximum propagation time, The maximum propagation time includes the duration during which the pulse probe signals of the plurality of pulse probe signals propagate from the laser light source and return to the receiver as they are conducted and pass through the last loopback furthest from the laser light source. Before the laser light source generates the second pulse probe signal immediately following the first pulse probe signal, each feedback signal of the first pulse probe signal is received by the receiver. The disturbance positioning method according to claim 12.

14. The characteristic of the aforementioned disturbance is the disturbance frequency. To generate power spectra for multiple feedback signals within a frequency range exceeding the aforementioned disturbance frequency range, Monitoring the time-dependent intensity of the power spectrum within the frequency range including the disturbance frequency, corresponding to the phase difference, This includes determining the location of the disturbance when the intensity exceeds a predetermined threshold, The power spectrum is monitored as a function of frequency and loopback position along the transmission system. The disturbance positioning method according to any one of claims 8 to 13.

15. A laser light source for transmitting multiple pulse probe signals, A polarization rotation device configured to rotate the polarization of the plurality of pulse probe signals, An optical transmission system including multiple loopbacks, configured to receive the multiple pulse probe signals and to guide the multiple pulse probe signals to pass through the multiple loopbacks, A receiver for receiving multiple feedback signals derived from multiple pulse probe signals from the optical transmission system, The receiver is coupled to a disturbance detection system, The disturbance detection system is configured to measure the phase difference between the polarizations of the feedback signal pairs of the plurality of feedback signals. The aforementioned feedback signal pair is received from the loopback pair of the plurality of loopbacks, The characteristic of each of the aforementioned multiple feedback signals is the phase of polarization rotation fed back from a predetermined loopback. The disturbance detection system is configured to determine the location of the disturbance by measuring the change in the value of the phase difference associated with the polarization returned from the adjacent loopback of the loopback pair. Track monitoring system.

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