Extending the range of dynamic acoustic sensing and positioning in submarine cables using loopback technology

Abstract

To provide systems and methods for extending a dynamic acoustic sensing range and localization in undersea cables using loopbacks.SOLUTION: A DAS transmission system 151 for extending a distributed acoustic sensing (DAS) range in undersea optical cables over multiple spans and for providing span-specific DAS information comprises a DAS interrogator 152, an outbound DAS signal path, a plurality of outbound amplifiers, a return signal path, a plurality of return amplifiers, a plurality of loopbacks 153, and a loopback component 166.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] [Cross - reference to Related Applications] This application claims the benefit of priority to a patent application for an invention entitled "EXTENDING DYNAMIC ACOUSTIC SENSING RANGE AND LOCALIZATION IN UNDERSEA CABLES USING LOOPBACKS" filed on June 23, 2021, with U.S. Provisional Patent Application No. 63 / 213978. Further, this application claims priority to a patent application for an invention entitled "EXTENDING DYNAMIC ACOUSTIC SENSING RANGE AND LOCALIZATION IN UNDERSEA CABLES USING LOOPBACKS" filed on June 15, 2021, with U.S. Provisional Patent Application No. 63 / 210775. The entire contents of these two applications are incorporated herein by reference.

[0002] Embodiments of the present disclosure relate to the field of optical communication systems. In particular, the present disclosure relates to techniques for extending the range of distributed acoustic sensing (DAS) in undersea optical cables using at least loopbacks.

Background Art

[0003] In distributed acoustic sensing (DAS) systems, optical cables can be used to provide real-time or near-real-time distributed distortion sensing. In other words, the cable itself can be used as a sensing element to detect or monitor different types of interruptions, interferences, irregularities, activities, naturally occurring events, acoustic vibrations, etc., in a DAS environment (e.g., a terrestrial environment, a submarine environment). To this end, an optoelectronic device coupled to the optical cable of a DAS system can detect and process reflected light signals (e.g., audio distortion signals) at a specific distance in the DAS environment.

[0004] Generally, a DAS interrogator unit can detect an optical fiber cable using coherent laser pulses, where the phase shift of the returned backscattered light signal is measured. As described, the optical phase shift between pulses can be proportional to the strain in the optical fiber, resulting in the ability to transmit vibrations, etc. For example, a DAS system can be based on Rayleigh scattering (it may also be called a Rayleigh scattering-based DAS system). In this system, coherent laser pulses can be transmitted along the optical fiber, and due to the scattering sites within the optical fiber, the optical fiber can function as a distributed interferometer, for example, having a gauge length approximately equal to the pulse length. The intensity of any reflected light can be measured as a function of time after the transmission of the laser pulse, and this is called coherent Rayleigh optical time-domain reflectometry (COTDR).

[0005] If a laser pulse has already traveled the entire length of the optical fiber and returned, the next laser pulse can be transmitted along the optical fiber. Changes in the reflected intensity of consecutive laser pulses from the same region of the optical fiber may be due to changes in the optical path length of that section of the optical fiber. Because DAS systems based on Rayleigh scattering are typically sensitive to both optical fiber strain and temperature changes, optoelectronic devices can perform measurements almost simultaneously across all sections of the optical fiber.

[0006] In Rayleigh scattering-based DAS systems, laser pulses are attenuated as they propagate along optical fibers. For a single-mode optical fiber operating at 1550 nm, a typical attenuation can represent an optical loss of approximately 0.2 dB / km. Because the laser pulse needs to make a double pass along the optical fiber, an optical loss of approximately 0.4 dB per kilometer of cable length can occur. Therefore, the "maximum range" of the optoelectronic device in a DAS system corresponds to the point where the amplitude of the reflected pulse becomes so low that the optoelectronic device can no longer obtain or decode a clear signal from it. Generally, the maximum range is approximately 40–50 km from the coupled optoelectronic device, or each time that range reaches a total optical loss of approximately 10–12 dB. In recent years, DAS has been applied to boreholes for seismic cross-section measurements of active sources, where, in many applications, a maximum range of several tens of kilometers may suffice.

[0007] In the case of optical fibers deployed in submarine communication cables, increasing attention is being paid to early warning of interference, including asset protection and prevention of external intrusions to submarine cables. As mentioned above, in principle, the sensitivity of DAS to distortion means that DAS technology can detect acoustic noise generated from sources such as ships, providing information on potential hazards and offering sufficient advance warning to respond to and prevent damage to the cable. However, in the case of long-distance underwater cables, the optical fiber span can be about 50km to 100km, and the underwater cable can continue to extend for hundreds to thousands of kilometers in total. Therefore, the DAS range and sensing capability of known DAS systems are significantly limited, and in many cases, the sensing range of a given DAS system is limited to a single optical fiber span. To overcome such limitations, a common DAS solution is to connect or link many independent optoelectronic devices to cover the desired range, with each of these independent optoelectronic devices monitoring the corresponding range-limited optical fiber span. Thus, each of the optoelectronic devices and the optical fibers coupled to them effectively form and function as a separate DAS system. Such conventional solutions are not only extremely expensive (for example, because extending the desired range requires an increasing number of independent optoelectronic devices and related components), but furthermore, this design is prohibited and impractical (and even impossible) in seabed or underwater environments or applications.

[0008] This disclosure provides the above and other considerations. [Brief explanation of the drawing]

[0009] [Figure 1] This is a diagram showing an example of an optical communication system. [Figure 2] This figure shows the architecture of a first DAS system according to an embodiment of the present disclosure. [Figure 3] This figure shows the architecture of a second DAS system according to an embodiment of the present disclosure. [Figure 3A]This figure shows the architecture of a third DAS system according to an embodiment of the present disclosure. [Figure 4] This figure shows the architecture of a fourth DAS system according to an embodiment of the present disclosure. [Figure 5] This figure shows the architecture of a fifth DAS system according to an embodiment of the present disclosure. [Figure 5A] This figure shows the architecture of a sixth DAS system according to an embodiment of the present disclosure. [Figure 6] This figure shows one scenario of DAS detection according to the embodiments of this disclosure. [Figure 7] This is a diagram illustrating the first example flowchart. [Figure 8] This figure shows a second example flowchart. [Figure 9] This is a diagram illustrating a third exemplary flowchart. [Modes for carrying out the invention]

[0010] The embodiments will now be described more comprehensively with reference to the drawings, which illustrate exemplary embodiments. The scope of the embodiments should not be construed as being limited to those described herein. On the contrary, these embodiments are provided to make the invention thorough and complete and to fully convey the scope of the invention to those skilled in the art. In the drawings, the same reference numeral always refers to the same component.

[0011] Before describing specific embodiments in detail with reference to the drawings, let's review the overall characteristics of these embodiments. They provide novel DAS devices, systems, and architectures that extend the range of DAS sensing capabilities, and in particular, span multiple spans of underwater systems, including underground optical cables. According to various embodiments, as discussed below, the range of DAS sensing is extended, and positioning capabilities are improved or maintained by providing return signal detection components for specific spans.

[0012] In several embodiments, techniques are provided for extending the distributed acoustic sensing (DAS) range within submarine optical cables. For example, the DAS range can be extended by the steps of transmitting and amplifying the DAS signal along multiple spans of a first optical fiber, routing or bypassing the DAS signal from the first optical fiber to a second optical fiber different from the first optical fiber via a high-loss loopback architecture, and returning and amplifying the DAS signal along the same multiple spans to a DAS device. The DAS device can then detect any changes in the DAS environment by receiving and processing the DAS signal. The loopback configuration can be based on different types of loopback architectures.

[0013] According to some embodiments, a DAS signal (e.g., an optical signal) can be transmitted from a first end of an optical cable by a DAS device (e.g., a DAS interrogator). This DAS signal may also be called a transmitted DAS signal. The transmitted DAS signal can propagate in a first direction along a first optical fiber of a dedicated optical fiber pair of optical cables and can be periodically amplified by one or more spaced optical amplifiers along the optical fiber. The optical amplifiers are provided to overcome the loss budget limitations of the DAS equipment, and a loopback with a return optical fiber path returns the DAS query signal to a DAS receiver. At a predetermined distance along the optical cable (e.g., after the "Nth" amplifier along the cable), the transmitted DAS signal can be returned to the DAS device by routing or bypassing the DAS signal to a second optical fiber of a dedicated optical fiber pair of optical cables using a high-loss loopback architecture. In this regard, due to the fact that each optical amplifier has an optical isolator that allows light to propagate in only one direction, a loopback is required to route the reflected DAS signal from a predetermined span through a return path to the DAS receiver (DAS interrogator).

[0014] A feature of the following embodiment is a DAS interrogator (DAS device) located at the end of an underwater optical cable containing multiple spans. For example, the spans can correspond to the distance between repeaters in an underwater communication system, where a given repeater includes at least one amplifier for amplifying the DAS signal in at least one direction. In various embodiments, the DAS signal is transmitted outbound along the optical cable via a dedicated DAS optical fiber pair. The outbound DAS signal is periodically amplified by an inline amplifier, where the DAS signal may be reflected in each span using a loopback architecture by Rayleigh backscattering (Lowry backscattering). In such a manner, according to some non-limiting embodiments, the reflected DAS signal from each span can be routed to a return optical fiber also configured with (multiple) inline amplifiers via loopback in each span.

[0015] The DAS range can be extended in a manner that is significantly advantageous and improved compared to conventional solutions by (i) transmitting and amplifying the DAS signal along multiple spans of a first optical fiber, (ii) routing or bypassing the DAS signal from the first optical fiber to a second optical fiber different from the first optical fiber via a high-loss loopback architecture, and (iii) returning the DAS signal along the same multiple spans to a DAS device for amplification. In conventional solutions, the DAS range is typically limited to a single optical fiber span (e.g., the range cannot be extended beyond the first amplifier), whereas the DAS range extension techniques described herein extend the DAS range beyond a single optical fiber span at least. Advantageously, the length of the range extension is flexible and variable; for example, the length of the DAS range extension can be designed and adjusted according to various use cases. Furthermore, since only a single DAS device is required, unlike conventional DAS systems with many DAS devices, at least the loopback architecture enables the use of the extended-range DAS system in submarine applications.

[0016] This embodiment provides a high query rate in a DAS system, regardless of the distance from the DAS device, enabling detection over a wide frequency range. In conventional DAS systems, the query rate F is limited by distance L to F = c / 2nL, where c is the speed of light and n is the refractive index. In the current embodiment of this disclosure, the query frequency may be limited by the amplifier span length La to F = c / 2nLa, but not by the distance L from the interrogator. Therefore, by simply providing an amplifier with a fixed span interval limited by La, the query rate can be kept at a value limited by the span length of the amplifier in an optical cable of any length with only one DAS interrogator at one end.

[0017] As will be described in more detail below, various embodiments provide a DAS system based on an optical fiber pair, where the DAS signal can be routed or bypassed from a first optical fiber to a second optical fiber of a bidirectional optical fiber pair based on different high-loss loopback architectures. In one example, the routing or bypass may be based on an output-to-output loopback architecture, in which a first end of the loopback optical fiber is coupled to the output of the amplifier of the first optical fiber, and a second opposite end of the loopback optical fiber is coupled to the output of the amplifier of the second optical fiber. In another example, the routing or bypass may be based on an output-to-input loopback architecture, in which a first end of the loopback optical fiber is coupled to the output of the amplifier of the first optical fiber, and a second opposite end of the loopback optical fiber is coupled to the input of the amplifier of the second optical fiber.

[0018] Therefore, the wider coverage provided by the extended DAS range enables the DAS system to better monitor underwater-related activities. For example, the optical cable of the extended DAS system can be used to intercept or monitor earthquakes, seabed movements, ship characteristics, ship passages, anchor drops, trawling of fishing nets, etc. At least for this reason, the optical cable effectively functions as a microphone to monitor potential events or problems that may occur on the seabed, such as intrusion or potential intrusion into the optical cable of an underwater optical communication system.

[0019] In various embodiments of the present disclosure, components are provided in the DAS system to provide detection of a specific span of the return signal to the DAS interrogator. As will be described in detail below, in some embodiments, in addition to the loopback between optical fiber pairs to provide detection of a specific span, the new DAS system includes an optical filter array including selective optical filters located in multiple spans of the underwater optical communication system. Such a configuration enables the DAS interrogator to receive a DAS signal at a specific wavelength, which is the characteristic of a specific filter in a specific span. In different embodiments, the optical filter may be tunable or fixed.

[0020] As will be further described in detail below, in different variations of the DAS system with an optical filter array, the DAS signal transmitted from the DAS interrogator may be transmitted at a single wavelength or along multiple wavelengths, where the predetermined wavelength is specified for a predetermined span of the underwater optical system. In a particular embodiment, when the DAS system operates at a single wavelength, the DAS frequency may be tuned to a frequency suitable for a specific span / optical filter, or alternatively, multiple tunable filters may be provided with different loopbacks along the underwater cable, whereby a predetermined tunable filter in a predetermined span can be appropriately tuned in or out to transmit or block the return signal received by the DAS interrogator.

[0021] In another embodiment, as will be described in detail below, the DAS system is configured such that multiple loopbacks are arranged between fiber optic pairs and an optical switch is arranged within the loopback path to receive DAS signals from a specific span of the underwater optical system. In such a manner, by turning on or off different switches provided in different loopbacks, any span can be interrogated separately.

[0022] By reference, various configurations of the DAS system according to different embodiments of the present disclosure are shown in FIGS. 2-5 below. According to various embodiments of the present disclosure, the DAS system can be integrated into an underwater optical communication system based on an optical cable, where communication is transmitted over multiple channels. The DAS system can be integrated with an optical communication system provided with bidirectional communication capabilities, as will be described in detail below with reference to FIG. 1. Also, FIG. 6 shows a general scenario for detecting and positioning disturbances using a DAS system with an extended range according to this embodiment.

[0023] Referring to the drawings, FIG. 1 shows an exemplary bidirectional optical communication system 101, which can transmit a large amount of data over a long distance using high-bandwidth optical fibers. Thus, the bidirectional optical communication system 101 can be considered a long-distance optical communication system. Bidirectional data transmission can be implemented by constructing fiber optic pairs within an optical cable and transmitting one or more channels (e.g., wavelength division multiplexing channels) for each fiber optic pair.

[0024] As shown, the optical communication system 101 may also include terminals 103 and 105 connected via two unidirectional optical paths 111 and 121, which together form a bidirectional optical fiber pair. Optical path 111 can transmit (multiple) signals, data, information, etc., in one direction (e.g., to the right) from the transmitter 113 at terminal 103 to the receiver 115 at terminal 105. Optical path 121 can transmit (multiple) signals, data, information, etc., in the other direction (e.g., to the left) from the transmitter 125 at terminal 105 to the receiver 123 at terminal 103.

[0025] With respect to terminal 103, optical path 111 is an outbound path and optical path 121 is an inbound path. Optical path 111 may include optical fibers 117-1 to 117-n and optical amplifiers 119-1 to 119-n, and optical path 121 may include optical fibers 127-1 to 127-n and optical amplifiers 129-1 to 129-n. Optical fibers 117-1 to 117-n and 127-1 to 127-2 may be segments of a single optical fiber 117 and a single optical fiber 127, respectively, where these segments are formed by coupling amplifiers to optical fibers 117 and 127, as shown.

[0026] In the examples, one or more of the optical amplifiers 119-1 to 119-n and 129-1 to 129-n may be erbium-doped optical fiber amplifiers (EDFAs). In some examples, the transmitter 113 and receiver 123 may be housed together at terminal 103 as a transponder or transceiver, and similarly, the transmitter 115 and receiver 125 may be housed together at terminal 105 as a transponder or transceiver.

[0027] An optical path pair (e.g., optical paths 111, 121) may be configured as a group of amplifier pairs 119-1 to 119-n and 129-1 to 129-n in repeaters 131-1 to 131-n connected or coupled via optical fiber pairs 117 (e.g., via 117-1 to 117-n) and 127 (e.g., via 127-1 to 127-n) (these optical fiber pairs may be contained in an optical fiber cable together with other optical fibers or optical fiber pairs supporting additional path pairs). Each repeater 131 may include at least two pairs of amplifiers 119, 129 for each path pair, and may also include additional amplifiers for additional path pairs.

[0028] The optical amplifiers 119 and 129 can be EDFA or other rare-earth doped optical fiber amplifiers, such as Raman amplifiers or semiconductor optical amplifiers (SOAs). The coupled paths 133-1 to 133-n can be coupled, for example, between one or more optical paths 111 and 121 in repeaters 131-1 to 131-n. The term "couple" or "coupled" as used in this invention broadly means any connection or connecting, coupling, link or link connection, direct or indirect, or wired or wireless connection, and does not necessarily mean that the coupled members or components are directly connected to each other.

[0029] In some embodiments, the DAS system can be integrated with an optical communication system 101, such as a DAS interrogator 102.

[0030] Figure 2 shows the architecture of a first DAS system, shown as DAS system 150 according to an embodiment of the present disclosure. As shown, DAS system 150 may include a DAS interrogator 152 coupled to a DAS transmission system 151, the DAS transmission system configured in a high-loss loopback architecture, with only one loopback, i.e., loopback 153, depicted. The DAS interrogator 152 may include a laser light source (not shown) to generate outbound DAS signals transmitted along the DAS transmission system 151. In this figure and other subsequent figures, outbound and return DAS signals can be transmitted along optical fibers, for example, as commonly described with respect to a bidirectional communication system 101. According to various embodiments, these optical fibers can be dedicated to DAS signal transmission and separated from the communication payload optical fibers of the optical cable. However, according to some embodiments, the DAS transmission system 151 can be integrated, at least partially, with a bidirectional optical communication system (e.g., bidirectional communication system 101). For example, components of the DAS transmission system 151 can be installed alongside components of the bidirectional communication system. For instance, the optical fiber of the DAS transmission system 151 can be installed alongside the common optical cable of the bidirectional communication system 101. Also, other components of the DAS transmission system 151 (e.g., EDFA) may or may not be installed alongside components of the bidirectional transmission system, for example, a repeater of the bidirectional communication system 101.

[0031] The DAS interrogator 152 may be configured to transmit an outbound DAS signal, receive a return DAS signal based on the outbound DAS signal, and process the received return DAS signal to extract acoustic characteristics or features of the seabed environment, at least partially based on the processing. In this respect at least, the DAS interrogator 152 may include appropriate hardware components (e.g., memory, one or more processors, interfaces, etc.) for generating, transmitting, receiving, and analyzing the returned DAS signal. In this embodiment and other subsequent embodiments, the outbound DAS signal can be transmitted as a series of pulses, where the return DAS signal is also represented as a series of pulses. The DAS interrogator 152 may be contained within a terminal or may be a standalone device.

[0032] The DAS interrogator 152 can be coupled to a first optical fiber, which provides a transmission path for the outbound DAS signal. When the DAS interrogator 152 transmits the outbound DAS signal, as shown in Figure 2, the outbound DAS signal propagates along the transmission path (typically to the right in the figure) and is periodically amplified by EDFAs 154, 156, and 158. As further shown, a loopback optical fiber can be provided, directed by a loopback 153. For example, the first end of the loopback optical fiber in loopback 153 can be coupled to the first optical fiber transmitting the outbound DAS signal at the coupling point, and the second end of the loopback optical fiber in loopback 153 can be coupled to a second optical fiber transmitting the return DAS signal at the coupling point, where the second optical fiber (shown in the lower path in Figure 2) provides a return path for the return DAS signal. In this example, the return loopback optical fiber is configured as a high-loss loopback path and / or provides a high-loss loopback path. Therefore, via the loopback optical fiber in loopback 153, the outbound DAS signal in the transmission path is routed or bypassed to a second optical fiber (return path), thereby the outbound DAS signal propagates along the return path as a return DAS signal, which may be amplified, for example, by at least the EDFA 160 as shown, and returned to the DAS interrogator 152.

[0033] It can be understood that the first and second optical fibers providing the transmission path and return path, respectively, may be included in a bidirectional optical fiber pair or may form a bidirectional optical fiber pair. In different embodiments, this optical fiber pair may be an independent DAS-dedicated optical fiber pair or a payload-carrying optical fiber pair, in which case the DAS signal may have a wavelength other than the payload channel wavelength so that the DAS signal does not interfere with the payload signal. It can be further understood that each "Nth" opposing group of amplifiers (e.g., the Nth amplifier coupled to the first optical fiber and the Nth amplifier coupled to the second optical fiber) may be paired and housed in the same repeater (e.g., similar to the repeater shown in Figure 1).

[0034] Furthermore, EDFA 162 and EDFA 164, shown in the return path of Figure 2, may be configured to amplify additional return DAS signals derived from the outbound DAS signal and route them through an additional loopback (not shown) of the optical transmission system 151.

[0035] In the arrangement shown in Figure 2, the span length between repeaters, expressed as the distance between EDFAs, may be approximately 50 km to 100 km, similar to conventional underwater optical transmission systems. Therefore, by providing an arrangement of multiple EDFAs, the DAS system 150 can provide DAS detection with an extended disturbance range using only the DAS interrogator 152, where the DAS detection is extended beyond the length of a single span, for example, to an extended range of multiple spans in an optical communication system.

[0036] To more clearly illustrate the advantages of this embodiment, Figure 6 shows a configuration 200 for extending the DAS range according to this embodiment. In the example of Figure 6, the optical transmission system 101 is depicted as a series of repeaters 506, 508, 510, 512, 514, and 516, where these repeaters may be equipped with conventional equipment for transmitting underwater optical communication in a bidirectional manner. In addition, the aforementioned components of a DAS system (e.g., DAS system 150) can be integrated into configuration 200, where, in some embodiments, the components of DAS system 150 may be co-located with the components of optical transmission system 101.

[0037] This allows outbound DAS signals to be transmitted from the DAS interrogator 152 (located on the coast), which propagates along the first optical fiber and is periodically amplified by the EDFAs (see Figure 2) of the DAS transmission system 151 (these EDFAs may be located at repeaters 506, 508, and 510), and routed or bypassed to a second optical fiber via one or more loopback optical fibers (not shown in Figure 6) located at the repeaters, thereby allowing the outbound DAS signals to be amplified in the reverse direction and returned to the DAS interrogator 152. Accordingly, the configuration of the loopback optical fiber at the location associated with repeater 510 allows the DAS range to be extended until approaching repeater 510, the configuration of the loopback optical fiber at the location associated with repeater 512 allows the DAS range to be extended until approaching repeater 512, the configuration of the loopback optical fiber at the location associated with repeater 514 allows the DAS range to be extended until approaching repeater 514, the configuration of the loopback optical fiber at the location associated with repeater 516 allows the DAS range to be extended until approaching repeater 516, and so on.

[0038] In some cases, the DAS transmission system 151 can be extended to the same extent as the bidirectional optical communication system 101. Thus, the bidirectional optical communication system 101 may be, for example, a transoceanic system with 80 repeaters spanning 6,000 km. Similarly, since the DAS transmission system 151 can span 80 of the same repeaters, activities occurring at any point along the underwater optical cable of the bidirectional optical communication system 101 can be monitored by the DAS interlogger 152. For example, if a vessel 520 conducts fishing activities beyond the ocean, such as between repeaters 514 and 516, these activities can be effectively monitored and analyzed by at least a further extended DAS range, as shown. Thus, the vessel 520 (e.g., ship acoustic features), activities (e.g., anchor drag, fishing net drag), and potential interference that the vessel may have with the optical cable of the optical communication system 101 can be monitored by at least a further extended DAS range, and such monitoring is advantageous over the usual limited DAS range discussed previously.

[0039] Returning to Figure 2, as shown, the loopback 153 provides a loopback component 166, which can regulate the transmission of the return DAS signal in the loopback 153. As will be described in detail below, an example of a loopback component 166 for regulating the transmission of the return DAS signal includes an optical filter or an optical switch. However, other components for regulating the return DAS signal are also possible. As will be described in detail with respect to the subsequent drawings, a loopback component such as the loopback component 166 can modify (including blocking) the (multiple) return DAS signals led to the DAS interrogator via the loopback in a manner that provides information about a specific loopback or a specific span regarding the return DAS signal, thereby contributing to better identification and positioning of disturbances near the DAS transmission system 151.

[0040] Next, turning to Figure 3, we see the architecture of a second DAS system, shown as DAS system 170 according to an embodiment of the present disclosure. DAS system 170 may share components in common with DAS system 150 described above, where the functions of these components may be similar to those described above. DAS system 170 comprises a DAS interrogator 152 and a DAS transmission system 171, the DAS transmission system comprising a plurality of EDFAs along both the outbound direction (top) and the return direction (bottom), as shown. In this figure, a plurality of loopbacks are depicted, including loopbacks 173 and 175. In some configurations, the outbound EDFAs and return EDFAs may be related by amplifier pairs, as shown in amplifier pair n (EDFA 156 and EDFA 162) and amplifier pair n+1 (EDFA 158 and EDFA 164).

[0041] In the operation following amplifier pair n, the outbound DAS signal can be routed back to the DAS interrogator 152 by routing the outbound DAS signal from the first optical fiber to the second optical fiber of the bidirectional optical fiber pair using a high-loss loopback architecture (indicated as loopback 173). The return DAS signal is then routed to pass through EDFA 162 and EDFA 160 before being received by the DAS interrogator 152.

[0042] Furthermore, after the n+1 amplifier pair, the outbound DAS signal can be routed by loopback 175 in a manner similar to routing by loopback 173, and a portion of the outbound DAS signal can be returned to DAS interrogator 152. The returned DAS signal is then routed to pass through EDFA 164, EDFA 162, and EDFA 160 before being received by DAS interrogator 152. The DAS transmission system 171 may also include other amplifier pairs, which may be spaced according to the span of the bidirectional optical communication system, as discussed. Thus, in some examples, the amplifier pairs may be spaced 50km, 70km, 90km, or similar distances from each other. In some examples, the amplifier pairs of the DAS transmission system may be co-located with repeaters of the bidirectional optical communication system. Thus, in a transoceanic cable, the DAS transmission system 171 may include dozens of amplifier pairs and associated loopbacks.

[0043] The DAS transmission system 171 further comprises an optical filter array including a predetermined optical filter associated with a predetermined loopback. In some embodiments, an optical filter can be provided for each loopback of the DAS transmission system 171. Figure 3 shows two of these optical filters, indicated as optical filter 172 (F n (Also indicated by), provided along the path of the first DAS return signal, associated with amplifier pair n and loopback 173, and optical filter 174 (F n+1A loopback (also indicated by ) is provided along the path of the second DAS return signal and is associated with amplifier pair n+1 and loopback 175. In various embodiments, each optical filter in the optical filter array is provided with a component for filtering and transmitting the return DAS signal having a center frequency of a specific span (loopback). In this manner, each loopback of the DAS transmission system 171 leads the return DAS signal to the DAS interrogator 152 at a specific frequency associated with the loopback. Furthermore, since a given loopback is associated with a given span along the DAS transmission system 171, the DAS interrogator 151 can perform DAS sensing of a particular span by querying the given DAS return signal at the frequency of the loopback filter associated with the span of interest. In other words, in order to provide DAS information positioned in a given span or loopback, it is possible to query not only the distance to multiple amplifier pairs provided by employing the DAS transmission system 171, but also the return DAS signal.

[0044] As described above, according to various embodiments, the DAS interrogator 152 can operate at a single wavelength or optical frequency. In the operation of the DAS system 170 according to one modification, the DAS frequency can be tuned to a frequency suitable for a particular span / optical filter of the DAS transmission system 171 to transmit or block the return DAS signal received by the DAS interrogator 152.

[0045] In operation using another modified configuration, the aforementioned optical filters (172, 174, etc.) can be provided as multiple tunable filters, and a given tunable filter in a given span can be appropriately tuned in or tuned out to transmit or block the return DAS signal received by the DAS interrogator 152.

[0046] Figure 3A shows the architecture of a third DAS system according to an embodiment of the present disclosure. DAS system 170-A can share most of the same components as DAS system 170, where DAS system 170-A can be considered a modification of DAS system 170. The main difference between the two DAS systems is that in the DAS system, loopback 173-A is equipped with EDFA 176, and loopback 175-A is equipped with EDFA 178. Other loopbacks of the DAS system (not shown) may similarly be equipped with corresponding bandpass filters and EDFAs. The two optical bandpass filters shown in loopbacks 173-A and 175-A (shown as bandpass filter 172-A and bandpass filter 174-A) may be similar to or the same as optical filter 172 and optical filter 174. In this embodiment, since each loopback of DAS system 190-A is equipped with a bandpass filter and EDFA, noise performance and query distance can be improved. In the example shown in Figure 3A, bandpass filters 172-A and 174-A are placed before EDFAs 176 and 178. In other embodiments, if the return path signal is too low for acceptable processing in the DAS interrogator, these filters may be placed after the corresponding EDFAs. In other words, such alternative placement of filters can be made to improve the noise performance of the return path EDFAs 176 and 178.

[0047] Next, turning to Figure 4, we see the architecture of a fourth DAS system, shown as DAS system 180 according to an embodiment of the present disclosure. DAS system 180 can share components common to DAS system 150 and DAS system 170 described above, where the functions of these components may be similar to those described above. The difference between DAS system 180 and DAS system 170 is that DAS system 180 provides a DAS interrogator 182 including a laser comb or similar structure.

[0048] During operation, the DAS interrogator 182 can generate an outbound DAS signal modulated by a laser comb, thereby transmitting the outbound DAS signal at multiple optical frequencies corresponding to multiple corresponding filter frequencies associated with the corresponding optical filters of different loopbacks of the DAS transmission system 171. In this manner, when the outbound DAS signal is routed through a predetermined loopback of the DAS transmission system 171, a predetermined portion of the outbound DAS signal corresponding to the transmission frequency of the optical filter of the loopback is returned to the DAS interrogator 182. Thus, the DAS interrogator 182 can simultaneously receive and query multiple DAS return signals, each associated with a different loopback. Furthermore, based on the frequency of a predetermined DAS return signal, the DAS interrogator can favorably associate each of the multiple simultaneously received return DAS signals with a specific span or loopback location of the DAS transmission system 171.

[0049] Figure 5 shows the architecture of a fifth DAS system, shown as DAS system 190 according to an embodiment of the present disclosure. DAS system 190 may share components common to DAS systems 150, 170, and 180 described above, where the functions of these components may be similar to those described above. DAS system 180 comprises a DAS interrogator 152 and a DAS transmission system 191, the DAS transmission system comprising a plurality of EDFAs along both the outbound direction (top) and the return direction (bottom), as shown. In this figure, a plurality of loopbacks are depicted, including loopbacks 173 and 175. In some configurations, the outbound EDFAs and return EDFAs may be related by amplifier pairs, as shown in amplifier pair n (EDFA 156 and EDFA 162) and amplifier pair n+1 (EDFA 158 and EDFA 164).

[0050] The DAS transmission system 191 includes an optical switch array, which includes a predetermined optical switch associated with a predetermined loopback. In some embodiments, an optical switch can be provided for each loopback of the DAS transmission system 191. According to various embodiments, the optical switches can be controlled on or off by mechanical, electrical, electromechanical, electro-optical, or other means.

[0051] Figure 5 illustrates two of these optical switches, indicated as optical switch 192, located along the path of the first DAS return signal and associated with amplifier pair n and loopback 173, and optical switch 194, located along the path of the second DAS return signal and associated with amplifier pair n+1 and loopback 175. In various embodiments, each optical switch in the optical switch array can be operated to turn on or off according to a control signal supplied by the DAS interrogator 192. In this manner, the DAS return signal routed through each loopback of the DAS transmission system 191 can be transmitted to the DAS interrogator 192, or interrupted and transmitted to the DAS interrogator 192, as needed.

[0052] During operation, according to some embodiments, the DAS interrogator 192 can transmit outbound DAS signals to the DAS transmission system 191 such that multiple DAS return signals are rerouted through a plurality of corresponding loopbacks. To query DAS return signals specified for a given span or loopback of the DAS transmission system 191, the DAS interrogator can transmit a group of on / off control signals to set the state of each optical switch in the loopback. For example, the group of on / off control signals may include a single switch-on signal for a target optical switch transmitted to the target loopback, or it may include multiple switch-off signals for all other optical switches transmitted to all other loopbacks of the DAS transmission system 191. In this manner, when transmitting outbound DAS signals, only one optical switch in the target loopback may be turned on so that the DAS signal is transmitted from the target loopback to the DAS interrogator 192, but no return DAS signals are received from other loopbacks of the DAS transmission system. This situation then facilitates individual DAS queries for each particular span of the DAS transmission system 191. Of course, in some scenarios, all optical switches may be set to the default off position, and the DAS interrogator 192 can send a single switch-on signal to the selected optical switch to individually query the target loopback associated with the selected optical switch.

[0053] In the scenario shown in Figure 5, optical switch 192 is ON and optical switch 194 is OFF. We can assume that other optical switches (not shown) of the DAS transmission system 191 are also OFF. Therefore, all return DAS signals (see, for example, return DAS signal 197), as well as the return DAS signal 195 routed to pass through loopback 173, are blocked by the corresponding OFF optical switches of the loopback.

[0054] Figure 5A shows the architecture of a sixth DAS system according to an embodiment of the present disclosure. DAS system 190-A can share most of the same components as DAS system 190, where DAS system 190-A can be considered a modification of DAS system 190. The main difference between these two DAS systems is that DAS system 190-A includes inline bandpass filters in each loopback of DAS system 190-A. In the example in Figure 5A, two bandpass filters are shown: filter 193 in loopback 173-B and filter 196 in loopback 175-B. These bandpass filters are arranged inline with the corresponding optical switches, as discussed above with reference to Figure 5. Note that the two optical bandpass filters shown in loopback 173-B and loopback 175-B (shown as bandpass filter 193 and bandpass filter 176) may be similar to or the same as optical filter 172 and optical filter 174. Furthermore, loopback 173-B is equipped with EDFA 198, and loopback 175-B is equipped with EDFA 199. Other loopbacks of the DAS system (not shown) may similarly be equipped with corresponding bandpass filters and EDFAs. In this embodiment, since each loopback of the DAS system 190-A is equipped with a bandpass filter and EDFA, noise performance and query distance can be improved. In the example in Figure 5A, the two bandpass filters are placed before EDFA 198 and EDFA 199. In other embodiments, if the return path signal is too low for acceptable processing in the DAS interrogator, these filters may be placed after the corresponding EDFAs. In other words, such alternative placement of filters can be used to improve the noise performance of the return path EDFAs 198 and EDFA 199.

[0055] Figure 7 shows an exemplary flowchart 700 according to an embodiment of the present disclosure. For example, the distributed acoustic sensing shown in flowchart 700 can be performed by a DAS interrogator, which may be coupled to a bidirectional optical fiber pair (e.g., a dedicated DAS optical fiber pair, or an existing optical system payload-carrying optical fiber pair). In block 702, the first outbound DAS signal is led along the DAS transmission system through the first optical fiber of the optical fiber pair. According to some embodiments, the optical fiber pair may be included in the DAS transmission system, which is at least partially located in a bidirectional optical communication system.

[0056] In block 704, the first return DAS signal, based on the first outbound DAS signal, is led or routed through a predetermined loopback of the DAS transmission system via a second optical fiber of the optical fiber pair.

[0057] In block 706, the first return DAS signal is filtered through a first optical filter associated with a predetermined loopback, where the filtered first return DAS signal is transmitted at a target optical frequency.

[0058] In block 708, the DAS interrogator is configured to receive the filtered first return DAS signal at a target optical frequency so that it can be appropriately processed and analyzed. In some examples, additional return DAS signals derived from the first outbound signal may be routed to the DAS interrogator via other loopbacks and an additional optical filter transmitted at an optical frequency other than the target optical frequency. In this manner, such additional DAS return signals can avoid interfering with the processing of the first filtered return DAS signal analyzed by the DAS interrogator.

[0059] Figure 8 shows an exemplary flowchart 800 according to another embodiment of the present disclosure. In block 802, outbound DAS signals are routed along the DAS transmission system through multiple optical fibers of the optical cable. In some examples, the DAS transmission system comprises multiple amplifier pairs, which can be distributed in the DAS transmission system at intervals of approximately 50 km to 100 km. In some examples, the amplifier pairs can be co-located with repeaters of a bidirectional optical communication system that can employ the same optical cable as the DAS transmission system for communication channels.

[0060] In block 804, a first return DAS signal based on an outbound DAS signal is directed or routed to pass through a selected loopback associated with a selected span of the DAS transmission system.

[0061] In block 806, a second return DAS signal based on the outbound DAS signal is directed or routed to pass through an additional loopback associated with an additional span of the DAS transmission system.

[0062] In block 808, the first return DAS signal is queried at the DAS interrogator by turning on the first optical switch at the selected loopback and turning off the second optical switch at the additional loopback. In some examples, the first return DAS signal can be queried individually by turning off all optical switches in the DAS transmission system at all loopbacks other than the selected loopback, thereby blocking the return optical fiber that conducts the DAS signals to the DAS interrogator once all return DAS signals other than the first return DAS signal have propagated to the DAS transmission system.

[0063] Figure 9 shows an exemplary flowchart 800 according to another embodiment of the present disclosure. In block 902, an outbound DAS signal is routed along the optical cable of the DAS transmission system at a plurality of selected optical frequencies. In block 904, a first return DAS signal based on the outbound DAS signal is routed or directed to pass through a predetermined loopback of the DAS transmission system at a first frequency within a group of selected optical frequencies.

[0064] In block 906, a second return DAS signal based on the outbound DAS signal is led or routed to pass through an additional loopback of the DAS transmission system at a second frequency within the selected optical frequencies of the group.

[0065] In block 908, the DAS interrogator is configured to simultaneously receive and process a first return DAS signal at a first frequency and a second return DAS signal at a second frequency.

[0066] In some examples, the operation of blocks 902-908 can be completed by generating an outbound DAS signal from a laser comb-like structure and transmitting the DAS signal at multiple optical frequencies, the multiple optical frequencies corresponding to multiple optical filter frequencies associated with corresponding optical filters located at a predetermined loopback and additional loopbacks. In this manner, when the outbound DAS signal is routed to pass through the predetermined loopback and additional loopbacks, a portion of the outbound DAS signal corresponding to the transmission frequencies of the predetermined loopback optical filter and additional loopback optical filter is returned to the DAS interrogator so as to be simultaneously received and / or processed.

[0067] This application discloses novel and inventive devices, systems, and techniques for extending the DAS range in multiple spans within an optical cable using loopback technology, including providing DAS information for a specific span. This disclosure is not limited in scope by the specific embodiments described herein. In practice, various other embodiments and improvements of this disclosure, in addition to those described herein, will be apparent to those skilled in the art from the above description and drawings.

[0068] Accordingly, other such embodiments and improvements are included within the scope of this disclosure. Furthermore, while this specification has described this disclosure in the context of specific embodiments for specific purposes in specific environments, those skilled in the art will recognize that its usefulness is not limited thereto and that this disclosure can be beneficially implemented for any number of purposes in any number of environments. Accordingly, the claims set forth below should be construed in accordance with the entire scope and spirit of the invention as described herein. 。 [Item 1] A DAS interrogator for transmitting outbound DAS signals, An outbound signal path for transmitting the outbound DAS signal over at least one outbound optical fiber, A plurality of outbound amplifiers coupled along the outbound signal path, wherein the plurality of outbound amplifiers are spaced apart from each other by a limited span distance, A return signal path for conducting multiple return DAS signals based on the outbound DAS signal through multiple return optical fibers, A plurality of return amplifiers coupled along the return signal path, wherein the plurality of return amplifiers are spaced apart from each other by a limited span distance, Multiple loopbacks for rerouting the outbound DAS signal between the outbound signal path and the return signal path to form the multiple return DAS signals, The system comprises a loopback component positioned on at least one of the plurality of loopbacks to coordinate the transmission of the return DAS signal from at least one loopback to the DAS interrogator, system. [Item 2] The aforementioned loopback component includes an optical filter, The system described in item 1. [Item 3] The loopback amplifier provided in the aforementioned loopback is further comprising The system described in item 2. [Item 4] The loopback component includes an optical switch that can be controlled on or off by a mechanical device, electrical device, electromechanical device, or electro-optical device. The system described in item 1. [Item 5] The loopback further comprises a loopback amplifier and a bandpass filter provided in the aforementioned loopback. The system described in item 4. [Item 6] The bandpass filter is placed between the loopback amplifier and the return signal path. The system described in item 5. [Item 7] At least some of the aforementioned outbound amplifiers, return amplifiers, or combinations thereof are erbium-doped optical fiber amplifiers, rare-earth-doped optical fiber amplifiers (other than erbium), Raman amplifiers, semiconductor optical amplifiers, or combinations thereof. The system described in item 1. [Item 8] Transmitting outbound DAS signals from a DAS interrogator over an outbound DAS signal path that includes at least one optical fiber, The outbound DAS signal is amplified by multiple outbound amplifiers along the outbound DAS signal path, and the multiple outbound amplifiers are distributed across multiple spans. The outbound DAS signal is routed to a plurality of loopbacks placed between the outbound DAS signal path and the return DAS signal path. Transmitting at least one return DAS signal from at least one of the plurality of loopbacks to the DAS interrogator along the return signal path, This includes amplifying the at least one return DAS signal, The at least one return DAS signal is processed by the at least one component located in the loopback so as to provide the DAS interrogator with DAS information for a specific span. method. [Item 9] An optical filter is provided in at least one of the plurality of loopbacks. The method described in item 8. [Item 10] The loopback amplifier is provided in at least one of the loopbacks. The method described in item 9. [Item 11] The optical switch is provided in at least one of the plurality of loopbacks, The optical switch can be controlled on or off by a mechanical device, an electrical device, an electromechanical device, or an electro-optical device. The method described in item 8. [Item 12] The loopback amplifier and bandpass filter provided in at least one of the loopbacks are further provided, The bandpass filter is placed between the loopback amplifier and the return signal path. The method described in item 11. [Item 13] At least some of the aforementioned outbound amplifiers, return amplifiers, or combinations thereof are erbium-doped optical fiber amplifiers, rare-earth-doped optical fiber amplifiers (other than erbium), Raman amplifiers, semiconductor optical amplifiers, or combinations thereof. The method described in item 8. [Item 14] A DAS interrogator for transmitting outbound DAS signals, An outbound signal path for transmitting the outbound DAS signal over at least one outbound optical fiber, A plurality of outbound amplifiers coupled along the outbound signal path, wherein the plurality of outbound amplifiers are spaced apart from each other by a limited span distance, A return signal path for conducting multiple return DAS signals based on the outbound DAS signal through multiple return optical fibers, A plurality of return amplifiers coupled along the return signal path, wherein the plurality of return amplifiers are spaced apart from each other by a limited span distance, Multiple loopbacks for rerouting the outbound DAS signal between the outbound signal path and the return signal path to form the multiple return DAS signals, A loopback component positioned in at least one of the plurality of loopbacks to coordinate the transmission of the return DAS signal from at least one loopback to the DAS interrogator, The system comprises an optical amplifier provided in at least one of the loopbacks, system. [Item 15] The aforementioned loopback component includes an optical filter or an optical switch. The system described in item 14.

Claims

1. A DAS interrogator for transmitting multiple outbound DAS signals having multiple optical frequencies, An outbound signal path for transmitting the plurality of outbound DAS signals over at least one outbound optical fiber, A plurality of outbound amplifiers coupled along the outbound signal path, wherein the plurality of outbound amplifiers are spaced apart from each other by a limited span distance, A return signal path for conducting multiple return DAS signals based on each of the multiple outbound DAS signals through multiple return optical fibers, A plurality of return amplifiers coupled along the return signal path, wherein the plurality of return amplifiers are spaced apart from each other by a limited span distance, Multiple loopbacks for rerouting each of the multiple outbound DAS signals between the outbound signal path and the return signal path to form the multiple return DAS signals, A loopback component having optical filters positioned at each of the loopbacks to coordinate the transmission of the plurality of return DAS signals from each of the plurality of loopbacks to the DAS interrogator, Equipped with, The optical filter frequency of each of the multiple optical filters corresponds to each of the multiple optical frequencies, system.

2. The system according to claim 1, wherein the optical filter frequencies of each of the plurality of optical filters are different from each other.

3. The system further comprises loopback amplifiers provided at each of the aforementioned plurality of loopbacks. The system according to claim 1 or 2.

4. At least some of the aforementioned outbound amplifiers, return amplifiers, or combinations thereof are erbium-doped optical fiber amplifiers, rare-earth-doped optical fiber amplifiers (other than erbium), Raman amplifiers, semiconductor optical amplifiers, or combinations thereof. The system according to claim 1 or 2.

5. The system according to claim 1 or 2, wherein the DAS interrogator includes a laser comb and transmits the plurality of outbound DAS signals modulated by the laser comb.

6. Transmitting multiple outbound DAS signals of multiple optical frequencies from a DAS interrogator in an outbound DAS signal path that includes at least one optical fiber, Each of the multiple outbound DAS signals is amplified by multiple outbound amplifiers along the outbound DAS signal path, and the multiple outbound amplifiers are distributed across multiple spans. Each of the aforementioned multiple outbound DAS signals is routed to a plurality of loopbacks placed between the outbound DAS signal path and the return DAS signal path, Transmitting multiple return DAS signals from each of the multiple loopbacks to the DAS interrogator along the return DAS signal path, This includes amplifying each of the plurality of return DAS signals, Each of the plurality of return DAS signals is processed by an optical filter located at each of the plurality of loopbacks to provide the DAS interrogator with DAS information of a specific span. The optical filter frequency of each of the multiple optical filters corresponds to each of the multiple optical frequencies, method.

7. The method according to claim 6, wherein the optical filter frequencies of each of the plurality of optical filters are different from each other.

8. A loopback amplifier is provided in each of the plurality of loopbacks. The method according to claim 6 or 7.

9. At least some of the aforementioned outbound amplifiers, return amplifiers, or combinations thereof are erbium-doped optical fiber amplifiers, rare-earth-doped optical fiber amplifiers (other than erbium), Raman amplifiers, semiconductor optical amplifiers, or combinations thereof. The method according to claim 6 or 7.

10. The method according to claim 6 or 7, wherein the DAS interrogator includes a laser comb and transmits the plurality of outbound DAS signals modulated by the laser comb.

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