Method and system for distributed optical fiber sensing

Abstract

A distributed fiber optic sensing (DFOS) method is disclosed. The method includes (a) repeatedly transmitting an interrogation optical signal to at least one optical fiber, (b) dispersively receiving a backscattered optical signal along at least one optical fiber, (c) combining the backscattered optical signal and an optical reference signal, (d) processing the combined signal to determine at least one polarization state change of the backscattered optical signal along at least one optical fiber, and (e) determining at least one birefringence event based on the at least one polarization state change.

Description

Technical Field

[0001] The present disclosure generally relates to systems and methods for distributed sensing based on one or more optical fibers. More particularly, aspects of the present disclosure relate to distributed polarization sensing (DPS) that detects one or more birefringence events, including one or more strain events and / or other noise caused, for example, by acoustics and weight, and separates these events from the background.

Background Art

[0002] Optical fiber sensing, more specifically distributed optical fiber sensing (DFOS), can detect the emission of sound and vibrations from objects and events in the surrounding area along at least one optical fiber. Also, DFOS can detect the physical movement of at least one optical fiber and / or the movement in the environment surrounding at least one optical fiber and identify the position. In an example where at least one optical fiber forms part of an optical fiber communication network, physical handling / movement of the optical fiber such as movement, tension, bending, torsion, etc. of the optical fiber and / or physical movement in the environment surrounding the optical fiber can lead to network errors, network flap events and / or network outages.

[0003] The mention of prior art in this specification does not admit or suggest that this prior art forms part of the common general knowledge in any jurisdiction, or that this prior art is understood by a person skilled in the art, considered relevant, and / or reasonably expected to be combined with other prior art, nor should it be so considered.

Summary of the Invention

[0004] A distributed fiber optic sensing (DFOS) system, components for DFOS, and related DFOS methods are described. The DFOS system and DFOS methods can be used to more easily distinguish between one or more birefringence events (which may further result in, for example, network error, stop, or flap events related to the physical handling of the optical fiber) that may include acoustic disturbances, strain activity caused by weight, and / or other detected noise, and the background.

[0005] A distributed fiber optic sensing (DFOS) method is described. The method includes: (a) repeatedly transmitting an interrogation optical signal to at least one optical fiber; (b) dispersively receiving a backscattered optical signal along at least one optical fiber; (c) combining the backscattered optical signal and an optical reference signal; (d) processing the combined signal to determine at least one polarization state change of the backscattered optical signal along at least one optical fiber; and (e) determining at least one birefringence event based on the at least one polarization state change.

[0006] In some embodiments, the DFOS method further includes distributed acoustic sensing (DAS) and processing the backscattered optical signals in parallel to determine at least one acoustic and / or weight-induced strain disturbance in addition to at least one birefringence event. In some embodiments, determining at least one acoustic disturbance is based on the spatial derivative of the phase difference between the backscattered optical signal and the optical reference signal.

[0007] In some embodiments, determining at least one birefringence event is based on at least one polarization state change exceeding a predetermined threshold.

[0008] In some embodiments, at least one optical fiber forms at least a part of an optical fiber communication network, and step (e) of paragraph

[0005] includes determining at least one network error or outage or flap event in the physical layer according to at least one birefringence event, which includes determining the location of at least one network error or outage or flap event. In some embodiments, the DFOS method further includes notifying a control center of at least one network error or outage or flap event associated with at least one birefringence event.

[0009] In some embodiments, step (c) of paragraph

[0005] includes splitting the backscattered optical signal into a first polarization channel and a second polarization channel orthogonal to the first polarization channel, splitting the optical reference signal into a third polarization channel parallel to the first polarization channel and a fourth polarization channel parallel to the second polarization channel, combining the first polarization channel of the backscattered optical signal and the third polarization channel of the optical reference signal, and / or combining the second polarization channel of the backscattered optical signal and the fourth polarization channel of the optical reference signal.

[0010] In some embodiments, the central frequency of the optical reference signal is different from the central frequency of the backscattered optical signal.

[0011] In some embodiments, determining at least one polarization state change is based on determining at least one of the instantaneous magnitude and the instantaneous phase change over time.

[0012] In some embodiments, at least one birefringence event is caused by an anisotropic stress applied to at least one optical fiber. In some embodiments, the anisotropic stress applied to at least one optical fiber is caused by at least one physical handling of at least one optical fiber including at least one of movement, tension, bending or torsion of at least one optical fiber.

[0013] A distributed fiber optic sensing (DFOS) system is described. The system includes an optical signal transmitter configured to repeatedly transmit interrogation optical signals to at least one optical fiber, and an optical signal receiver configured to receive and disperse backscattered optical signals along at least one optical fiber, the optical signal receiver including at least one optical combiner configured to combine the backscattered optical signal and an optical reference signal, and at least one photodetector configured to provide an electrical signal based on the combined optical signal; and a processing system configured to process the electrical signal to determine at least one polarization state change of the backscattered optical signal along at least one optical fiber and to determine at least one birefringence event based on the at least one polarization state change. Including.

[0014] In some embodiments, the DFOS system further includes distributed acoustic sensing (DAS), and the processing system is further configured to process the backscattered optical signals in parallel to determine at least one acoustic and / or gravity-induced strain disturbance in addition to at least one birefringence event. In some embodiments, determining at least one acoustic disturbance is based on the spatial derivative of the phase difference between the backscattered optical signal and the optical reference signal over a spatial region of the optical fiber.

[0015] In some embodiments, determining at least one birefringence event is based on at least one polarization state change exceeding a predetermined threshold.

[0016] In some embodiments, at least one optical fiber forms at least a part of an optical fiber communication network, and the processing system is further configured to determine at least one network error or outage or flap event in the physical layer according to at least one birefringence event, which includes determining the location of at least one network error or outage or flap event. In some embodiments, the processing system is further configured to notify a control center of at least one network error or outage or flap event associated with at least one birefringence event.

[0017] In some embodiments, the DFOS system further includes a first optical polarizer configured to split a backscattered optical signal into a first polarization channel and a second polarization channel orthogonal to the first polarization channel, and a second optical polarizer configured to split an optical reference signal into a third polarization channel parallel to the first polarization channel and a fourth polarization channel parallel to the second polarization channel, and at least one optical combiner includes at least one of a first optical combiner configured to combine the first polarization channel of the backscattered optical signal and the third polarization channel of the optical reference signal, and a second optical combiner configured to combine the second polarization channel of the backscattered optical signal and the fourth polarization channel of the optical reference signal.

[0018] In some embodiments, the center frequency of the optical reference signal is different from the center frequency of the backscattered optical signal.

[0019] In some embodiments, determining at least one polarization state change is based on determining at least one of an instantaneous magnitude and an instantaneous phase change over time.

[0020] In some embodiments, at least one birefringence event is caused by anisotropic stress applied to at least one optical fiber. In some embodiments, the anisotropic stress applied to at least one optical fiber is caused by physical handling of at least one optical fiber including at least one of movement, tension, bending, or torsion of the at least one optical fiber.

[0021] A method is also described. The method includes (a) repeatedly transmitting an interrogation optical signal to at least one optical fiber, (b) dispersively receiving a backscattered optical signal along the at least one optical fiber, (c) combining the backscattered optical signal and an optical reference signal, (d) processing the combined signal to determine at least one polarization state change of the backscattered optical signal along the at least one optical fiber, (e) determining at least one birefringence event based on the at least one polarization state change, (f) determining that the at least one birefringence event is caused by physical handling of the at least one optical fiber, and (g) notifying a control center of the at least one birefringence event and / or the physical handling of the at least one optical fiber associated with the at least one birefringence event.

[0022] In some embodiments, step (e) of paragraph

[0021] includes determining the location of the at least one birefringence event, and / or step (f) of paragraph

[0021] includes determining the location of the physical handling of the at least one optical fiber. In some embodiments, step (g) of paragraph

[0021] further includes notifying the control center of (1) the location of the at least one birefringence event and / or (2) the location of the physical handling of the at least one optical fiber associated with the at least one birefringence event.

[0023] In some embodiments, the method further includes (h) determining at least one network error or stop or flap event in the physical layer according to at least one birefringence event, which includes determining the location and time of at least one network error or stop or flap event. In some embodiments, the method includes notifying a control center of at least one network error or stop or flap event in the physical layer as an alternative or addition to (i) (1) at least one birefringence event, and / or (2) the physical handling of at least one optical fiber.

[0024] In some embodiments, the method further includes (j) determining the responsibility for at least one network error or stop or flap event in the physical layer. In some embodiments, step (j) includes processing non-distributed optical fiber sensing (non-DFOS) data. In some embodiments, the processing of non-DFOS data includes correlating the non-DFOS data with DFOS data obtained from backscattered optical signals based on time and / or position information.

[0025] In some embodiments, the non-DFOS data includes (1) visual information captured by one or more visual media capture devices / systems, and / or (2) log data recorded by a control center regarding the physical handling of at least one optical fiber.

[0026] In some embodiments, the non-DFOS data indicates at least one event and / or person responsible for at least one network error or stop or flap event in the physical layer.

[0027] The method is also described. This method includes: (a) determining at least one birefringence event occurring at a position along at least one optical fiber based on distributed fiber optic sensing (DFOS) data; (b) processing the DFOS data in combination with non-DFOS data; and (c) determining one or more causes of an error or outage or flap event of at least one network related to at least one birefringence event based on the result of step (b).

[0028] In some embodiments, step (b) of paragraph

[0027] includes correlating the non-DFOS data with the DFOS data based on time and / or position information.

[0029] In some embodiments, the non-DFOS data includes (1) visual information captured by one or more visual media capture devices / systems, and / or (2) log data recorded by a network operation center regarding the physical handling of at least one optical fiber.

[0030] In some embodiments, the non-DFOS data indicates events and / or responsible parties involved in an error or outage or flap event of at least one network in the physical layer.

[0031] In some embodiments, the method further includes (d) notifying a control center of an error or outage or flap event of at least one network and / or one or more causes of an error or outage or flap event of at least one network.

[0032] In some embodiments, the method further includes (e) providing feedback information related to iterative improvement of one or more ways of handling the optical fiber to reduce network exposure to the threat of an error or outage or flap of at least one network.

[0033] Further embodiments will be apparent from the following description, by way of example, with reference to the accompanying drawings.

Brief Description of the Drawings

[0034]

Figure 1

Figure 2A

Figure 2B

Figure 2C

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Embodiments for Carrying Out the Invention

[0035] References to fiber optic sensing in this disclosure should be construed to include any propagating wave or signal that gives a detectable change in the optical properties of a sensing optical fiber. These propagating waves or signals detected in a DFOS system include, among others, acoustic signals, seismic waves, vibrations, stress on the fiber core, and signal types that include one or more of very low frequency (DC type) signals that change slowly, such as gravity-induced compression waves that induce changes in local strain of the optical fiber. The basic sensing mechanism in one of the preferred embodiments is the result of the photoelastic effect, but there are other sensing mechanisms that can be utilized in this disclosure within the optical fiber, such as the thermo-optic effect and the magneto-optic effect.

[0036] The inventors of the present application have discovered that the physical handling / movement of an optical fiber can be associated with the polarization information of an optical signal transmitted within the optical fiber. However, conventional DFOS methods and / or systems do not utilize polarization information and may rely, for example, on distributed acoustic sensing (DAS) that depends on the vibration of a cable. As a result, the physical handling / movement of an optical fiber that causes minor vibrations may not be distinguishable from background noise induced by other more dominant acoustic disturbances and / or vibrations and may therefore not be detected by conventional DFOS methods and / or systems such as DAS. This disclosure can provide a DFOS method and system for detecting or separating such physical handling / movement of an optical fiber to identify its location, thus providing or reducing the rapid diagnosis of subsequent network errors, network flap events, and / or network outages. In addition, this disclosure can provide a DFOS method and system for improving the signal-to-noise ratio of backscattered signals based on distributed polarization sensing (DPS).

[0037] FIG. 1 shows an exemplary configuration of a DFOS system 100. The blocks (in FIG. 1 or in the figures of other systems of the present disclosure) represent the functional components of the DFOS system 100. It will be understood that the functions can be provided by separate or integrated physical components. The DFOS system 100 includes an optical signal transmitter 102 that transmits an optical signal 101 in the form of, for example, an optical pulse that is repeatedly transmitted to at least one optical fiber 110A, 110B, …, 110N. The at least one optical fiber 110A, 110B, …, 110N can be dispersed over a geographical area. In some embodiments, the at least one optical fiber can form part of an established dedicated optical fiber communication network. Techniques for reusing optical fibers that form part of an established dedicated optical fiber communication network are described in International Patent Application PCT / AU2017 / 050985 (published as International Publication No. WO 2018 / 045433), the entire contents of which are incorporated herein by reference.

[0038] In some embodiments, an optical signal 101 is provided to at least one optical amplifier 104, resulting in an overall amplification of the optical signal, i.e., an amplified optical signal 103, and an extended range of the interrogation signal. In one example, the at least one optical amplifier 104 includes an erbium-doped fiber amplifier (EDFA). The at least one optical amplifier 104 may be a single-stage amplifier or a multi-stage optical amplifier. In some embodiments, an optical attenuator (not shown) may be used after the at least one optical amplifier 104 to adjust the power of the amplifier output. In some embodiments, the at least one optical amplifier 104 is omitted. The DFOS system 100 may also include an optical circulator 106 configured to direct the optical signal 101 or the amplified optical signal 103 as an interrogation optical signal 105 to at least one optical fiber (110A, 110B, …, 110N). In some examples, the interrogation optical signal 105 can include a series of pulses each having a power of 0.1 to 10 mW (such as, but not limited to, 0.1, 0.24, 2.8, 5.78, 8, 9.45, and 10 mW) and a duration of 1 to 100 ns (such as, but not limited to, 1.23, 4, 25.7, 40.68, 80, 92.3, 99.31, and 100 ns).

[0039] The optical circulator 106 also receives a backscattered return optical signal 107 along at least one optical fiber (110A, 110B, …, 110N) and outputs the backscattered optical signal 109 to an optical signal receiver 108. FIG. 2A shows an exemplary return optical signal 107 including two orthogonal polarization channels (e.g., vertical polarization channels 202, 206 and horizontal polarization channels 204, 208) over a spatial region, i.e., an optical distance representing a position along the optical fiber. In particular, plots 202 and 204 show the magnitudes of the horizontal and vertical polarization channels, respectively, and plots 206 and 208 show the phases of the horizontal and vertical polarization channels, respectively.

[0040] FIG. 2B shows an exemplary return optical signal 107 including two orthogonal polarization channels (e.g., vertical polarization channel 107V and horizontal polarization channel 107H) in the time domain (plots 210 and 212), i.e., as a function of time. FIG. 2C shows the exemplary return optical signal 107 including two orthogonal polarization channels (e.g., vertical polarization channel 107V and horizontal polarization channel 107H) in the spatio-temporal domain (plots 214, 216, 218, and 220). In particular, plot 210 shows the exemplary magnitudes of the vertical polarization channel 107V and the horizontal polarization channel 107H of the return optical signal 107. Plot 212 shows the exemplary phases of the vertical polarization channel 107V and the horizontal polarization channel 107H of the return optical signal 107. Plots 214 and 216 are density plots showing the magnitudes of the vertical polarization channel 107V and the horizontal polarization channel 107H respectively over time and optical distance. Plots 218 and 220 show the phases of the vertical polarization channel 107V and the horizontal polarization channel 107H respectively over time and optical distance. In the example of FIGS. 2A, 2B, and 2C, the optical fiber terminates at approximately 37 km. The return optical signal 107 can be scattered and backscattered along the length of at least one optical fiber (110A, 110B, …, 110N) (e.g., via Rayleigh backscattering or other similar scattering phenomena).

[0041] The backscattered optical signal 109 reaching the optical signal receiver 108 as a function of the time after fiber transmission has a time dependence on the traveled optical fiber distance. The round-trip (i.e., outgoing and return) travel time of the backscattered optical signal 109 is used to multiplex the optical fiber over a series of linear channel positions across the entire optical fiber path. It will be appreciated that other devices may be used to connect the optical signal receiver 108 and at least one optical fiber (110A, 110B, …, 110N), including but not limited to optical circulators. The optical signal receiver 108 may also receive an optical reference signal 111 for detecting the backscattered optical signal 109. In some embodiments, the optical reference signal 111 is provided by the optical signal transmitter 102. The optical signal transmitter 102 and the optical signal receiver 108 can form a coherent optical time domain reflectometer (C-OTDR) (regardless of the presence or absence of the optical amplifier 104 and the optical circulator 106).

[0042] FIG. 3 shows an exemplary configuration of the optical signal transmitter 102 and a first exemplary configuration of the optical signal receiver 108A of the DFOS system of FIG. 1. In FIG. 3, the same components and features as those described with reference to FIG. 1 are denoted by the same reference numerals.

[0043] In the example shown in FIG. 3, the optical signal transmitter 102 includes at least one laser 302 to provide the light 301. In some embodiments, the at least one laser 302 includes a narrowband continuous wave (CW) laser module that is typically in the C-band or L-band. The optical signal transmitter also includes an optical beam splitter that provides a first portion of the light 301 (i.e., light 303) for DFOS and a second portion of the light 301 (e.g., an optical local oscillator signal) as the optical reference signal 111. The inset 321 in FIG. 3 shows exemplary optical intensities of the light 301, 303, and the optical reference signal 111 over time. In some embodiments, the optical reference signal 111 can be provided by a local oscillator light source independent of the at least one laser 302 (not shown). In one example, the local oscillator light source operates at the same wavelength as the at least one laser 302 for homodyne detection. In another example, the local oscillator light source operates at a different wavelength from the at least one laser 302 for heterodyne detection. The light 303 is supplied to the modulator 306. The modulator 306 is configured to control the power, frequency, phase, shape, polarization, and / or spatial direction of the interrogation optical signal 101. The inset 322 in FIG. 3 shows an example of an exemplary optical intensity plot of the interrogation optical signal 101 over time. In an example of heterodyne detection (the optical reference signal can be provided by the at least one laser 302 or an independent local oscillator light source), the modulator 306 can be used to shift the frequency of the interrogation optical signal so that the center frequency of the interrogation optical signal is different from the frequency of the optical reference signal, thereby avoiding DC noise in the detection stage. Various types of modulators can be used, including but not limited to acousto-optic modulators and electro-optic modulators. The modulator 306 then outputs the modulated optical signal (i.e., the optical signal 101) for amplification and / or interrogation.

[0044] Figure 3 also shows a first exemplary configuration of an optical signal receiver 108A that can be used in the DFOS system 100. In this example, the optical signal receiver 108A includes an optical combiner 308 configured to combine the backscattered optical signal 109 and the optical reference signal 111 and output a composite optical signal 305. The optical signal receiver 108A also includes at least one photodetector 310 configured to receive the composite optical signal 305 and output an electrical signal 307 representing the composite optical signal 305. The electrical signal 307 may be in the form of a current proportional to the composite amplitude (or intensity) of the two electric fields of the backscattered optical signal 109 and the optical reference signal 111 (i.e., E BS and E LO ). The two electric fields can be mathematically expressed in the following forms respectively.

[0045]

Number

[0046] where E LO (n,t) is the electric field of the optical reference signal 111 at the position n of the optical fiber (i.e., optical fiber channel n) at time t, and E BS (n,t) is the electric field of the backscattered optical signal 109 arriving from the position n of the optical fiber (i.e., optical fiber channel n) at time t.

[0047]

Number

Number

[0048]

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Number

[0049] The time-dependent superposition (combination) (i.e., the composite optical signal 305) of the optical reference signal 111 and the backscattered optical signal 109 in at least one photodetector 310 produces an electrical signal 207 (i.e., photocurrent (I)) of the following form.

[0050]

Number

[0051] where ΔΦ is the phase difference between the optical reference signal 111 and the backscattered optical signal 109, indicating the change in the local phase, and Δω is the difference between the instantaneous carrier frequency of the optical reference signal 111 and the backscattered optical signal 109, which is called the carrier frequency of the electrical signal 307. As shown in Equation (3), the electrical signal 207 includes four terms, the first two of which (i.e.,

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Number

[0052] FIG. 5 shows a first exemplary process 500 executed by the processing system 120. At step 502, the processing system receives a digital electrical signal 113. In some embodiments, the digital electrical signal 113 is stored in a storage unit (not shown) at step 502. The storage unit can include volatile memory such as random access memory (RAM) for the processing system 120 to execute instructions, calculate, operate on, or otherwise process data. In addition to or instead of this, the storage unit can include non-volatile memory such as one or more hard disk drives for the processing system 120 to store data before, after, and / or for later retrieval in signal processing. The processing system 120 and the storage unit may be distributed among a number of physical units and may include remote storage and potential remote processing such as cloud storage and cloud computing. In addition to or instead of storing the digital electrical signal 113, the backscattered optical signal 109 may be digitized, received by the processing system 120 at step 502, and stored as raw optical data (i.e., demodulated data derived from the optical signal) at step 504.

[0053] In some embodiments, a carrier frequency signal (e.g., the positive carrier frequency signal of Equation 3) can be removed by a filter such as a high-pass filter in step 506. Next, in step 508, the carrier frequency signal is down-converted to baseband (i.e., from the carrier frequency to the DC frequency). In step 510, the instantaneous magnitude and / or phase information of the complex components in the down-converted signal is obtained. For example, the down-converted signal can be sent to a rectangular-to-polar converter, where the input is the real and imaginary components and the output is the instantaneous magnitude and phase angle of the polar vector in the complex domain. Analysis of the instantaneous magnitude and / or instantaneous phase angle of the down-converted signal provides a time series of how the polarization state changes along the optical fiber. At least one change in the polarization state is determined in step 512, for example, based on the instantaneous magnitude and / or phase information. That is, each of the positive and negative carrier frequency signals contains information about the magnitude and local phase (i.e., the position along the optical fiber path) of each optical fiber channel, which provides the basis for distributed polarization sensing (DPS), so that at least one large polarization state change is detected and the position is identified. In some embodiments, at least one large polarization state change is defined as at least one polarization state change exceeding a predetermined threshold (e.g., 1 krad / s).

[0054] Small polarization state change events (e.g., 1 rad / s to 10 krad / s) are within the range of coherent transponder tracking (e.g., 1 rad / s to 10 Mrad / s), and thus, engineers in the telecommunications field will understand that they are less likely to cause network outages. However, these events may be related to the physical handling / movement of optical fibers associated with network errors, network flap events, and / or network outages in a telecommunications network. Therefore, the sensitivity of the disclosed DPS method to detect the physical handling / movement of optical fibers, as well as associating the physical handling / movement of optical fibers with network errors, network flap events, and / or network outages, can be an advantage of the disclosed DPS method.

[0055] In telecommunications, a network flap event or a route flap event occurs when the destination or route of a data packet changes suddenly or becomes unavailable and then becomes available again within a short period. Flap events are seen at the network level, but as described above, they may ultimately be caused by errors introduced along optical fibers or devices within individual parts of the network. For example, when a telecommunications system engineer maintains an optical fiber cable, as may occur dozens of times a day, especially in urban areas, the engineer often moves loops of excess telecommunications cable stored in underground pits to access a particular fiber junction. This physical activity can cause a change in the state of the environment of at least one optical fiber, which can lead to network errors, network flap events, and / or network outages. For example, if an error occurs across one optical fiber, the flow of packets through this part of the network will be distorted, and adjacent routers may recalculate the next route hop for this packet. The longer it takes to recalculate the new path for the stalled packet, the greater the risk of network flap events, service latency, and, in some cases, network outages.

[0056] The ultimate cause and location of network error / stop / flap events are usually unknown at the time of the failure. In some cases, the ultimate cause is a hardware error, software error, node - to - node interface error, configuration error, intermittent error caused by physical movement in at least one optical fiber, or an unreliable connection within the network. Any of these errors can cause the specific router's addressing and availability information to be repeatedly advertised or withdrawn. Depending on the specific network topology and protocol (link - state routing, distance - vector routing, route aggregation, etc.), the associated risk of errors cascading into network flap events can vary. For example, link - state routing protocols can generally be sensitive to network errors because each node calculates its routing table independently.

[0057] In communication networking, several strategies are commonly deployed to reduce network flap events and improve customer service. The first strategy is to adjust networking technologies such as route damping and route aggregation. This strategy can be implemented top - down across the network. For example, route damping penalizes, in an automated way, network route segments that have historically caused flaps by suppressing packet traffic passing through these segments for a predefined period. The second strategy is layer 1 hardening, which physically inspects and corrects misaligned or problematic devices, device connections, optical fibers, optical fiber joints, and / or optical fiber slices to remove network flaps. The third strategy is to deploy network monitoring services and network operation centers to register and respond to activities in real - time when activity information becomes available.

[0058] In some embodiments, the physical handling of at least one optical fiber, including movement, tension, bending, and / or torsion of the at least one optical fiber, may apply anisotropic stress to the core of the optical fiber, resulting in refractive index anisotropy, so-called birefringence. The polarization state of the interrogation optical signal 105 that undergoes this birefringence changes accordingly. Thus, the DFOS system 100 can be used to detect at least one large polarization state change and identify a location by analyzing at least one of the carrier frequency signals of the digital electrical signal 113 that includes information regarding the magnitude and local phase of the backscattered optical signal 109 at each optical fiber channel (i.e., a position along the optical fiber path). In step 514, the processing system 120 can be configured to determine at least one birefringence event based on at least one polarization state change. In embodiments where at least one optical fiber forms at least a part of an optical fiber communication network, the processing system 120 is further configured to determine at least one network error, outage, or flap event according to at least one birefringence event and identify a location. As a result, the present disclosure can facilitate or mitigate a rapid diagnosis of subsequent network errors, network flap events, and / or network outages, for example, by implementing at least one of the strategies described above.

[0059] The electric field amplitudes of the backscattered optical signal 109 and the optical reference signal 111 are independent and random, so there may be an optical fiber channel (i.e., a position along at least one optical fiber) where the intensity recorded due to destructive interference becomes zero. This can lead to the local phase information at the corresponding fiber position becoming irrecoverable. This is called optical fading. To solve this problem of optical fading, the DFOS system 100 can use a polarization-diverse receiver 108B, such as shown in FIG. 4. The optical signal receiver 108B splits the backscattered optical signal 109 into a first polarization channel 401V (whose electric field is

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[0060]

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[0061] The polarization diversity receiver 108B further includes at least one of a first optical combiner 406 and a second optical combiner 408. The first optical combiner 406 is configured to combine a first polarization channel 401V of the backscattered optical signal 109 and a third polarization channel 403V of the optical reference signal 111 to output a first composite optical signal 405. The second optical combiner 308 is configured to combine a second polarization channel 401H of the backscattered optical signal 109 and a fourth polarization channel 403H of the optical reference signal 111 to output a second composite optical signal 407. The composite optical signals 405 and 407 are respectively supplied to a first photodetector 410 and a second photodetector 412. By the time-dependent superposition (combination) of the optical reference signal 111 and the polarization channels of the backscattered optical signal 109 having equal polarization (i.e., the composite optical signals 405 and 407 respectively) in the respective first and second photodetectors 410 and 412, electrical signals 409 and 411 in the form of

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[0062]

Number

[0063] Part of the electrical signals 409 and / or 411 (e.g., positive or negative carrier frequency signals), or the entire electrical signals 409 and / or 411 can be digitized by the first ADC 414 and / or the second ADC 416 respectively, and these ADCs output the digital quadrature polarization signals 113V and 113H to the processing system 120 respectively for further processing and / or analysis (in step 502). In some embodiments, the digital quadrature polarization signals 113V and / or 113H are stored in a storage unit (not shown) in step 504. In addition to or instead of storing the digital quadrature polarization signals 113V and / or 113H, the backscattered light signal 109, and / or at least one of the first and second polarization channels 401V and 401H can be digitized, received in step 502, and stored as raw optical data (i.e., data obtained from the demodulated local signal) in step 504.

[0064] Since the positive and negative carrier frequency signals in Equation 8 or Equation 9 are the same, only the positive carrier frequency signal can be processed for further analysis. In some embodiments, the positive carrier frequency signal of Equation 8 and / or Equation 9 can be removed by a filter such as a high-pass filter in step 506. Next, in step 508, the positive carrier frequency signal is down-converted to baseband (i.e., from the carrier frequency to the DC frequency). This step can be achieved by multiplying the in-phase component and the quadrature component. In step 510, the instantaneous magnitude and / or phase information of the complex components in the down-converted signal is obtained. For example, the down-converted signal can be sent to a rectangular-polar coordinate converter, where the input is the real and imaginary components, and the output is the instantaneous magnitude and phase angle of the polar coordinate vector in the complex domain. It will be understood that the instantaneous phase angle accumulates over time, but its trend can be determined based on the time derivative. In some embodiments, the signal-to-noise ratio of the received electrical signal can also be improved using the time average of the complex components in the received electrical signal (before or after digitization).

[0065] Analysis of the instantaneous magnitude and / or instantaneous phase angle of a down-converted signal representing at least one of the orthogonal optical channels (i.e., 401V and 401H) provides a time series of how the polarization state changes along the optical fiber. At least one polarization state change is determined in step 512, for example, based on the instantaneous magnitude and / or phase information. A polarization state change detected at any location within the DFOS system is the cumulative effect of polarization state changes encountered along the outgoing and back-propagating paths. In step 514, the processing system 120 is further configured to determine at least one birefringence event based on at least one polarization state change. In embodiments where at least one optical fiber forms at least a portion of an optical fiber communication network, the processing system 120 is further configured to determine at least one network error, outage, or flap event according to at least one birefringence event and identify the location.

[0066] As described above, at least one birefringence event may be caused by anisotropic stress applied to at least one optical fiber, which anisotropic stress may result from physical handling of at least one optical fiber, including at least one of movement, tension, bending, or torsion of the at least one optical fiber. Although the polarization state of the interrogation optical signal 105 at the fiber location experiencing the birefringence event is random, it is assumed to vary linearly as it travels along the optical fiber, so at least one of the returning orthogonal polarization channels is piecewise smooth in time and space. At any one fiber location, small changes in magnitude and / or phase angle in at least one of the orthogonal polarization channels are consistent with piecewise smooth behavior, while significant changes in magnitude and / or phase angle indicate a large step change in the polarization state (referred to as a forward coupling event). Detection and localization of at least one polarization change form the basis for detecting and localizing physical handling / movement of the optical fiber, and thus warning of potential network error / stop / flap events associated with physical handling / movement of the optical fiber, or providing risk assessment. In some embodiments, at least one large polarization state change is defined as at least one polarization state change exceeding a predetermined threshold (e.g., 1 krad / s).

[0067] FIG. 6 shows exemplary digital electrical signals for two different polarization channels (e.g., 113V and 113H) obtained from a proof-of-concept experiment. In particular, FIG. 6 shows the magnitude of the baseband signals for two different polarization channels as a function of time. In this example, the first birefringence event occurred between 12 and 19 seconds, the second birefringence event occurred between 29 and 36 seconds, and the third birefringence event occurred between 48 and 54 seconds. Next, the time dependence of the travel distance of the optical fiber can be used to identify the location of the first and / or second and / or third birefringence events and to detect and locate potential network error / stop / flap events. Also, it can be seen that the two different polarization signals are amplified by different amounts by the first, second, and third birefringence events because one polarization state decelerates while the other polarization state accelerates. As a result of the birefringence event, the magnitudes of the two polarization signals are separated by a random amount, resulting in a total phase shift at the fiber location beyond the location of the birefringence event.

[0068] In some embodiments, the DFOS method and system with the aforementioned DPS capabilities can also be integrated with distributed acoustic sensing (DAS) capabilities. FIG. 7 shows a second exemplary process 700 executed by the processing system 120. In FIG. 7, steps and features similar to those described with reference to FIG. 5 are denoted with similar reference numerals. In process 700, the processing system 120 is configured in parallel to determine at least one acoustic disturbance caused by at least one object and / or event in step 702. Since the down-converted signal is already in a form that includes acoustic information and enables acoustic analysis, additional lower-level processing involving hardware / FPGA can be avoided. By combining the capabilities of both DPS and DAS to record complementary information, the need to deploy a second system and / or a second optical fiber can also be avoided. Techniques for determining at least one acoustic disturbance, including examples of at least one acoustic disturbance, are described in International Patent Application PCT / AU2019 / 051249 (published as International Publication No. WO 2020 / 097682), the entire content of which is incorporated herein by reference.

[0069] In other examples, the spatial differentiation of the backscattered optical signal over the optical fiber spatial region is used for DAS processing. The spatial differentiation of the phase in the first polarization state is

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[0070]

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[0071] [Number]

[0072] That is, the step of spatial differentiation acts to subdivide the received optical signal by an increment of a predetermined length (i.e., dz) for spatial differentiation. This length is called the gauge length and can be any length, but is generally on the order of a few meters. In some embodiments of DAS processing, the spatial differentiation of two orthogonally polarized optical signals can be combined in the complex domain to obtain a total phase measurement value (ΔΦ(n,t)).

[0073] [Number]

[0074] In some embodiments, further processing steps include (a) taking a phase average over a certain space or time, and / or (b) measuring the deviation from the phase average.

[0075] Figure 8 shows an exemplary density plot 800 of electrical signals generated by the DFOS system from a demonstration experiment. The detection in the demonstration experiment is recorded on a fully embedded optical fiber at intervals of 3.2 m. The horizontal axis (labeled "Optical distance [km]") represents the position along the optical fiber, the vertical axis (labeled "Time [s]") represents time, and the gray-scale amplitude of the plot represents the backscatter intensity. In this example, the birefringence event test included simulations of 5-second birefringence changes separated by repeating a pause of about 10 seconds three times. Due to the forward coupling resulting from combining two orthogonally polarized signals, the associated signal (i.e., shown by trace 702) extends from the location of the birefringence test at about 1.4 km to the end of the 4.5 km optical fiber. In Figure 8, features such as a trace of a straight line (e.g., 806) with a relatively constant gradient are associated with objects moving at a relatively constant speed (the gradient indicates the speed) that cause the associated acoustic disturbances and events detected by the DFOS system 100. Figure 8 further shows a trace 804 indicating a heavy object (e.g., a truck) that moves slowly during the first few seconds and then stops, causing a weight-induced strain detected by the DFOS system 100. The technique for detecting weight-induced strain data is described in International Patent Application PCT / AU2019 / 051249 (published as International Publication No. WO 2020 / 097682), which is incorporated herein by reference.

[0076] It can be seen from and / or understood from Figure 8 that the disclosed method and / or system can detect one or more birefringence events that generate small vibrations, acoustic disturbances, and / or weight-induced strain activities. In particular, the disclosed method and / or system can facilitate better discrimination between one or more birefringence events that may include acoustic disturbances, weight-induced strain activities, and / or other detected signals and the background. These events cannot be easily discriminated from such a background when sensed using DAS technology. This may be particularly desirable for applications in high-density / busy areas such as urban areas.

[0077] Accordingly, the disclosed DFOS method and system can provide real-time updates regarding the state of threats across an electrical communication network. In some embodiments, the disclosed DFOS method and system are used to determine at least one birefringence event and determine that the at least one birefringence event is caused by the physical handling of at least one optical fiber. Next, the at least one birefringence event and / or the physical handling of at least one optical fiber associated with the at least one birefringence event can be notified to a control center. The location and / or time of the at least one birefringence event, and / or the physical handling of at least one optical fiber associated with the at least one birefringence event can also be notified to the control center. In some embodiments, the disclosed DFOS method and system are used to determine at least one network error, outage or flap event in the physical layer according to at least one birefringence event, which includes determining the location of the at least one network error, outage or flap event. In this regard, next, the at least one network error, outage or flap event and its location can be notified to the control center.

[0078] This enables the rapid determination of the physical handling / movement of the optical fiber, and thus the determination of the root cause of network errors / stops / flaps that occur in the physical layer, generally within a few meters rather than at higher layers (i.e., determining which pits in the field and / or which cabinets in the data center are the locations of network errors / stops / flaps). This also enables a handoff of responsibility such that the causal relationship between the occurrence of a stop / error / flap and the agent that caused it is spatiotemporally linked. Handoff of responsibility can provide the advantage of being able to disrupt the agent that causes the flap before it escalates to a stop. Also, agents / technicians can know that their activities are being directly monitored and / or can improve their methods of handling the optical fiber more carefully through feedback of information provided by the disclosed DFOS methods and / or systems, such as during inspection of the pits. Thus, handoff of responsibility can also provide the advantage of strengthening the physical layer (i.e., layer 1) over time. In other words, the disclosed DFOS methods and systems can be used to iteratively improve and strengthen the physical network's exposure to threats of network errors / stops / flaps. By combining the capabilities of both the DPS and DAS to record complementary information, the need to deploy a second system and / or a second optical fiber can be avoided.

[0079] In some embodiments, the DFOS method and system can be used in combination with one or more non-DFOS methods and systems to detect, locate, and / or notify of the cause of one or more network errors / stops / flaps. That is, DFOS data can be used in combination with other non-DFOS data to detect, locate, determine, and / or notify of the cause of one or more network errors / stops / flaps.

[0080] One or more non-DFOS systems include those that use artificial vision means, which apply techniques such as machine vision to collect visual information for detecting and identifying movement and related events. For example, a closed-circuit television (CCTV) camera can be used for monitoring purposes. Each CCTV camera can always provide a local view of a street map with a depth of field determined by the optical system of the CCTV camera. As another example, a millimeter-wave radar system can be used to image dynamic objects (e.g., one or more technicians) within an area with relatively high movement accuracy. As yet another example, satellite imagery can provide an aerial view of an entire city of objects within the line of sight that the satellite does not obstruct. As yet another example, one or more light detection and ranging (LiDAR) systems overlooking one or more urban areas can be used. Next, the visual information captured as non-DFOS data can be processed and analyzed together with DFOS data by correlating it with DFOS data based on, for example, time and / or position information to determine errors / stops / flaps in one or more networks. For example, the disclosed DFOS system identifies birefringence events occurring at specific positions along an optical fiber. A DFOS system using DAS capabilities can also identify events related to the detected birefringence events. Visual information captured by one or more visual media capture devices / systems (e.g., CCTV cameras) monitoring that specific position and / or time can be analyzed, which indicates at least one event and / or a person related to the detected birefringence event.

[0081] In addition to or instead of this, one or more non-DFOS systems include those using a Network Operations Center (NOC) capable of recording log data including pit visits and / or activities. For example, the disclosed DFOS system identifies birefringence events occurring at specific locations and specific times along an optical fiber. A DFOS system using DAS capabilities can also identify events associated with the detected birefringence events. Information recorded by the NOC, such as pit visits and / or activities related to the optical fiber, can be timestamped and correlated with DFOS data based on time and / or location information to analyze this information, which indicates at least one event and / or a person associated with the detected birefringence event.

[0082] As described above, these can determine the root cause of one or more network errors / halts / flaps and thus can enable establishing responsibility, i.e., identifying the person responsible for one or more network errors / halts / flaps.

[0083] It will be understood that the invention, as disclosed and defined herein, extends to all alternative combinations of two or more distinct features mentioned or apparent from the text or drawings. All of these different combinations constitute various alternative aspects of the invention.

Claims

1. Distributed optical fiber sensing (DFOS) method, (a) Repeatedly transmitting a query optical signal through at least one optical fiber, (b) Dispersing and receiving backscattered light signals along at least one optical fiber, (c) Combining the backscattered light signal and the optical reference signal, (d) Processing the combined signals to determine at least one change in polarization state of the backscattered light signal along the at least one optical fiber, (e) Determining at least one birefringence event based on the at least one change in polarization state, A method that includes this.

2. The DFOS method according to claim 1, further comprising dispersive acoustic sensing (DAS) and processing the backscattered light signal in parallel to determine at least one acoustic and / or weight-induced strain distortion in addition to the at least one birefringence event.

3. The DFOS method according to claim 2, wherein determining the at least one acoustic disturbance is based on the spatial derivative of the phase difference between the backscattered light signal and the optical reference signal.

4. The DFOS method according to claim 1, wherein determining the at least one birefringence event is based on the at least one polarization state change exceeding a predetermined threshold, and the at least one birefringence event is caused by an anisotropic stress on the at least one optical fiber.

5. The at least one optical fiber forms at least a part of the optical fiber communication network. Step (e) includes determining an error, stop, or flap event in at least one network in the physical layer according to the at least one birefringence event, which includes determining the location of the error, stop, or flap event in at least one network. The method includes notifying the control center of an error, outage, or flap event of the at least one network related to the at least one birefringence event. The DFOS method according to claim 1.

6. The step (c) is: The backscattered light signal is divided into a first polarization channel and a second polarization channel orthogonal to the first polarization channel. The optical reference signal is divided into a third polarization channel parallel to the first polarization channel and a fourth polarization channel parallel to the second polarization channel. Combining the first polarization channel of the backscattered light signal and the third polarization channel of the optical reference signal, and / or Combining the second polarization channel of the backscattered light signal and the fourth polarization channel of the optical reference signal, The DFOS method according to claim 1, including the method described in claim 1.

7. The DFOS method according to claim 1, wherein determining the at least one change in polarization state is based on determining at least one of instantaneous magnitude and instantaneous phase changes over time.

8. A distributed optical fiber sensing (DFOS) system, An optical signal transmitting device configured to repeatedly transmit query optical signals through at least one optical fiber, An optical signal receiving device configured to receive backscattered light signals in a dispersed manner along at least one optical fiber, At least one optical combiner configured to combine the backscattered light signal and the optical reference signal, A photodetector configured to provide an electrical signal based on the combined optical signals, Including an optical signal receiving device, A processing system, The electrical signal is processed to determine at least one change in polarization state of the backscattered light signal along the at least one optical fiber. Based on the aforementioned change in polarization state, at least one birefringence event is determined. A processing system configured as follows, A system that includes this.

9. The DFOS system according to claim 8, further comprising distributed acoustic sensing (DAS), wherein the processing system is further configured to process the backscattered light signals in parallel to determine at least one acoustic and / or weight-induced distortion fault in addition to the at least one birefringence event.

10. The DFOS system according to claim 9, wherein determining the at least one acoustic interference is based on the spatial derivative of the phase difference between the backscattered light signal and the optical reference signal across the spatial domain of the optical fiber.

11. The DFOS system according to claim 8, wherein determining the at least one birefringence event is based on the at least one polarization state change exceeding a predetermined threshold, and the at least one birefringence event is caused by anisotropic stress on the at least one optical fiber.

12. The at least one optical fiber forms at least a part of the optical fiber communication network. The processing system is further configured to determine an error, stop, or flap event in at least one network in the physical layer according to the at least one birefringence event, which includes determining the location of the error, stop, or flap event in at least one network. The processing system is further configured to notify the control center of any error, stoppage, or flap event of the at least one network related to the at least one birefringence event. The DFOS system according to claim 8.

13. A first optical polarizer configured to split the backscattered light signal into a first polarization channel and a second polarization channel orthogonal to the first polarization channel, A second optical polarizer configured to split the optical reference signal into a third polarization channel parallel to the first polarization channel and a fourth polarization channel parallel to the second polarization channel, The further includes, the at least one optical combiner, A first optical combiner configured to combine the first polarization channel of the backscattered light signal and the third polarization channel of the optical reference signal, and A second optical combiner configured to combine the second polarization channel of the backscattered light signal and the fourth polarization channel of the optical reference signal, The DFOS system according to claim 8, comprising at least one of the above.

14. The DFOS system according to claim 8, wherein the center frequency of the optical reference signal is different from the center frequency of the backscattered light signal.

15. The DFOS system according to claim 8, wherein determining the at least one change in polarization state is based on determining at least one of instantaneous magnitude and instantaneous phase changes over time.

16. The DFOS method according to claim 4, wherein the anisotropic stress on the at least one optical fiber is caused by physical handling of the at least one optical fiber, including at least one of movement, tension, bending, or torsion of the at least one optical fiber.

17. Further comprising notifying a control center of the physical handling of the at least one birefringence event and / or the at least one optical fiber related to the at least one birefringence event, The DFOS method according to claim 16.

18. Determining the location of the at least one birefringence event, and / or The DFOS method according to claim 4, further comprising determining the physical handling location of the at least one optical fiber.

19. The DFOS method according to claim 18, wherein notifying the control center of the at least one birefringence event and / or the physical handling of the at least one optical fiber related to the at least one birefringence event includes notifying the control center of the location of the at least one birefringence event and / or the location of the physical handling of the at least one optical fiber related to the at least one birefringence event.

20. Further comprising determining responsibility for an error, outage, or flap event in the physical layer of the at least one network, Determining the aforementioned responsibility involves processing non-distributed optical fiber sensing (non-DFOS) data, and processing the non-DFOS data involves correlating the non-DFOS data with DFOS data obtained from the backscattered light signal based on time and / or location information. The DFOS method according to claim 16.

21. The DFOS method according to claim 19, wherein the non-DFOS data includes (1) visual information captured by one or more visual media capture devices / systems, and / or (2) log data recorded by the control center with respect to the physical handling of the at least one optical fiber.

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