Acoustic sensing for multispan sensing using single-wavelength optical frequency domain reflection method

Abstract

This invention discloses an acoustic sensing method for multispan sensing using a single-wavelength optical frequency domain reflection method. [Solution] A system and method for monitoring an optical transmission path in an optical transmission system. The optical transmission system comprises a sensing and interrogation unit and a plurality of sensing units located on the optical transmission path. An optical signal is transmitted to the plurality of sensing units to determine the state of one or more portions of the optical transmission path. A plurality of reflected signals in response to the optical signal are received. The plurality of reflected signals are converted in at least one of the frequency domain and the time domain. The state of one or more portions is determined using the converted plurality of reflected signals.

Description

[Technical Field]

[0001] This disclosure relates, in general terms, to optical fiber communication systems, particularly to distributed acoustic sensing, and more specifically to distributed acoustic sensing for multispan sensing using a single-wavelength optical frequency domain reflection method. [Background technology]

[0002] Distributed acoustic sensing (DAS), which uses telecommunications optical fibers as distributed sensors, is used to continuously detect spatial interference in real time along one or more long-distance transmission / sensing optical fibers. Conventional DAS distributed sensing systems are limited to performing sensing over optical fiber lengths of approximately 50-100 km (e.g., extended to 150 km in research units for available products). Such systems typically include a DAS interrogator unit (IU), which includes a DAS transmitter, a DAS receiver, and one or more repeater erbium-doped fiber amplifiers (EDFAs) that can be used to amplify one or more signals transmitted to the IU. However, conventional systems cannot sense multispan links using such series amplifiers. Some conventional systems use multiple DAS units operating at different wavelengths. Additionally, wavelength-related optical loopback paths are used to sense the span, and optical bandpass filters are used for filtering and / or selecting specific wavelengths for reverse transmission. This makes submarine optical path systems using the above sensing techniques more expensive, and because most repeaters are sole, it is difficult to remember backup units.

[0003] For example, a DAS system may be based on Rayleigh backscattering (also called a Rayleigh scattering-based DAS system). In this system, a coherent laser pulse can be transmitted along an optical fiber, and due to the scattering sites within the optical fiber, the optical fiber can function as a dispersive interferometer, for example, its gauge length being approximately equal to the pulse length. The intensity, frequency, and / or phase of any reflected light can be measured as a function of time after the laser pulse has been transmitted, which is called a coherent optical time-domain reflectometer (COTDR).

[0004] In some conventional systems, telecommunications optical fibers are used as distributed sensors to continuously detect spatial interference along long-distance transmission / sensing optical fibers in real time. However, typical sensing systems generally require multiple distributed acoustic sensing interrogation units operating at different wavelengths to sense different parts of the optical fiber, and the sensing system can become substantially more structural and operationally complex, especially if there are interfering elements along the cable (e.g., optical amplifiers), potentially leading to a higher error rate for the data channel. [Overview of the project] [Means for solving the problem]

[0005] In some embodiments, the present subject relates to an optical communication system. The system may comprise a sensing and interrogation unit and a plurality of sensing units, which are located to the sensing and interrogation unit using an optical communication path and are communicatively coupled to the sensing and interrogation unit. The sensing and interrogation unit may be configured to transmit an optical signal to the plurality of sensing units, receive a plurality of reflected signals in response to the optical signal, convert the plurality of reflected signals in at least one of the frequency domain and time domain, and use the converted plurality of reflected signals to determine the state of one or more parts.

[0006] In some embodiments, the present subject may include one or more of the following optional features: The optical signal may be a single-wavelength optical signal.

[0007] In some embodiments, multiple reflected signals may be transformed in the frequency domain to determine one or more positions corresponding to the approximate positions of reflected signals included in a plurality of reflected signals in an optical communication path. The plurality of reflected signals transformed in the frequency domain may be transformed in the time domain to determine one or more changes in the reflected signals over a predetermined time period and to determine the precise positions of the reflected signals. The transformation of the reflected signals in the frequency domain and the time domain may be performed by a Fast Fourier Transform. The plurality of reflected signals may include at least a portion of a first plurality of reflected signals received in a first time period and at least a portion of a second plurality of reflected signals received in a second time period, the second time period being a time period after the first time period.

[0008] In some embodiments, the sensing and interrogation unit may include a transmission optical device configured to transmit optical signals to a plurality of sensing units.

[0009] In some embodiments, the transmission device may include a laser light source configured to generate an optical signal. The laser light source may include at least one of a scanning laser, a continuous-wave laser, a multi-tone frequency laser, and any combination thereof.

[0010] In some embodiments, the sensing and interrogation unit may include a receiving optical device configured to be communicatively coupled to an optical transmission path and to receive multiple reflected signals.

[0011] In some embodiments, the optical communication path may be a distributed acoustic sensing optical transmission path.

[0012] In some embodiments, the optical signal may include an interrogation signal.

[0013] In some embodiments, the present subject is a method for monitoring an optical transmission path in an optical transmission system. The optical transmission system may comprise a sensing and interrogation unit and a plurality of sensing units located on the optical transmission path. The method may include transmitting an optical signal to the plurality of sensing units, receiving a plurality of reflected signals in response to the optical signal, converting the plurality of reflected signals in at least one of the frequency domain and time domain, and determining the state of one or more parts using the converted plurality of reflected signals.

[0014] In some embodiments, the present subject may include one or more of the following optional features: The optical signal may be a single-wavelength optical signal. The multiple reflected signals may be transformed in the frequency domain to determine one or more positions corresponding to the approximate positions of the reflected signals included in the multiple reflected signals in the optical communication path. The multiple reflected signals transformed in the frequency domain may be transformed in the time domain to determine one or more changes in the reflected signals over a given time period and to determine the precise positions of the reflected signals. The transformation of the reflected signals in the frequency domain and the time domain may be performed by a Fast Fourier Transform. The multiple reflected signals may include at least a portion of a first plurality of reflected signals received in a first time period and at least a portion of a second plurality of reflected signals received in a second time period, the second time period may be a time period after the first time period.

[0015] In some embodiments, the sensing and interrogation unit may include a transmitting optical device configured to transmit optical signals to a plurality of sensing units, and a receiving optical device configured to be commutably coupled to an optical transmission path and to receive a plurality of reflected signals.

[0016] In some embodiments, the transmission device may include a laser light source configured to generate an optical signal, and the laser light source may include at least one of a scan laser, a continuous wave laser, a multi-tone frequency laser, and any combination thereof.

[0017] Details of one or more variations of the subject matter described in this document are set forth in the drawings and the description below. Other features and advantages of the subject matter described in this document will be apparent from the specification, the drawings, and the claims.

Brief Description of the Drawings

[0018] The drawings incorporated herein and constituting a part of this specification illustrate some aspects of the subject matter disclosed in this document and, together with the specification, contribute to an understanding of some of the principles associated with the disclosed embodiments.

[0019] [Figure 1] An exemplary optical communication system is shown. [Figure 2] FIG. 2a shows an example of a repeater coupled to a high-loss loopback (which can be coupled to the system shown in FIG. 1). FIG. 2b shows an example of a repeater. [Figure 3] FIGS. 3a and 3b show diagrams depicting the relationship between the beat frequency and time in a receiver. [Figure 4a] An exemplary optical communication system according to some embodiments of the present subject matter is shown and can be used to determine the state of one or more portions (e.g., spans) of an optical communication path. [Figure 4b] An example of the signal flow of a data channel in the optical communication system shown in FIG. 4a according to some embodiments of the present subject matter is shown. [Figure 4c] An example of the signal flow of a DAS channel in the optical communication system shown in FIG. 4a according to some embodiments of the present subject matter is shown. [Figure 5] An exemplary windowed FFT technique according to some embodiments of the present subject matter is shown. [Figure 6a]This document presents an exemplary process for performing a windowed FFT by an interrogation and sensing unit and / or terminal according to several embodiments of the current subject. [Figure 6b] This presents another exemplary process for performing a windowed FFT by an interrogation and sensing unit and / or terminal according to several embodiments of the current subject. [Figure 7a] Examples of FFT processes with sliding windows applied, based on several embodiments of the current subject, are shown. [Figure 7b] Examples of FFT processes with sliding windows applied, based on several embodiments of the current subject, are shown. [Figure 8] This document presents an exemplary process for performing a sliding window FFT using an interrogation and sensing unit and / or terminal according to several embodiments of the present subject. [Figure 9-1] Figures 9a and 9b show various embodiments of the repeater that can be implemented in the system shown in Figure 4a according to several embodiments of the present subject. [Figure 9-2] Figure 9c shows various embodiments of a repeater that can be implemented in the system shown in Figure 4a, according to several embodiments of the present subject. [Figure 10] Another embodiment of a repeater that can be implemented in the system shown in Figure 4a, according to several embodiments of the present subject, is shown. [Figure 11] The process is illustrated by several embodiments of the current subject. [Figure 12] This section presents an exemplary system in several embodiments of the current subject. [Modes for carrying out the invention]

[0020] To address these and other potential shortcomings of currently available solutions, one or more embodiments of the present subject matter may also provide a sensing and interrogation unit for a multispan acoustic sensing system, which may include a transmitter and a receiver, and in particular a sensing and interrogation unit capable of performing multispan sensing in an optical communication system using a single-wavelength optical signal.

[0021] In conventional distributed acoustic sensing (DAS) systems, a DAS signal (e.g., an optical signal) can be transmitted from an outbound 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 any other pair of optical fibers in the optical cable, bidirectional, dedicated, and / or optical cable, and can be periodically amplified by one or more spaced optical amplifiers along the optical fiber. Unless otherwise limited, an optical fiber pair may refer to an actual optical fiber pair, separate cores and / or modes within the same optical fiber pair, and / or one or more bidirectional transmitted signals in the same core, and / or any other type of optical fiber pair.

[0022] In some cases, a DAS system can extend its DAS range by providing submarine optical cables. For example, the DAS range can be extended by transmitting and / or amplifying the DAS signal along multiple spans of a first optical fiber, routing and / or bypassing the DAS signal from the first optical fiber to a second optical fiber that may be different from the first optical fiber via, for example, a high-loss loopback (HLLB) architecture and / or an amplified filtered loopback (AFLB) architecture, and returning and / or amplifying the DAS signal to a DAS device along the same multiple spans. The DAS device can then detect and / or determine any changes in the DAS system environment by receiving and processing the DAS signal. Alternatively, the transmitted DAS signal can be returned to the DAS device by routing and / or bypassing the DAS signal to a second optical fiber of the optical fiber pair in the optical cable using, for example, an HLLB or AFLB architecture, at a predetermined distance along the optical cable (e.g., after the "Nth" amplifier along the optical cable).

[0023] Therefore, the wider coverage provided by the extended DAS range allows the DAS system to better monitor seabed-related activities. For example, the optical cables of the extended DAS system can be used to detect ("hear") and / or monitor earthquakes, seabed movements, ship features, ship passages, anchoring, fishing net drag, etc. Thus, the optical cables can effectively function as microphones to monitor potential problems and / or difficulties that may occur on the seabed, such as attacks and / or potential attacks on the optical cables of underwater optical communication systems.

[0024] In the following description, the term "path and / or link" may refer to any type of communication coupling and / or connection, and may include, but is not limited to, optical coupling and / or connection, electrical coupling and / or connection, electro-optical coupling and / or connection, electromechanical coupling and / or connection, electro-optical-mechanical coupling and / or connection, and / or any other type of coupling and / or connection capable of sending and receiving any type of signal.

[0025] Figure 1 shows an exemplary optical communication system 100, comprising two optical fibers forming a bidirectional optical fiber pair, distributed optical amplifiers provided in two directional optical communication paths, and optical links between the two directional paths in each amplifier pair. System 100 can transmit and receive large amounts of data over long distances using high-bandwidth optical fibers. The bidirectional optical communication system 100 may also be called a long-distance optical communication system. Bidirectional data transmission can be achieved by constructing optical fiber pairs, cores, and / or modes within an optical cable, and / or transmitting one or more channels (e.g., wavelength division multiplexing channels) per optical fiber pair.

[0026] System 100 may include terminals 103 and 105 that are communicatively coupled using (for example, unidirectional) optical paths 111 and 121. Terminal 103 may include a transmitter 113 and a receiver 123. Similarly, terminal 105 may include a receiver 115 and a transmitter 125. The transmitter 113 of terminal 103 can be communicatively coupled to the receiver 115 of terminal 105 via path 111. The transmitter 125 of terminal 105 can be communicatively coupled to the receiver 123 of terminal 103 via communication path 121. Paths 111 and 121 can form a bidirectional optical fiber pair. For example, optical path 111 can transmit one or more signals, data, information, etc., and / or any combination thereof in one direction (for example, from transmitter 113 to receiver 115). The optical path 121 can transmit one or more signals, data, information, etc., and / or any combination thereof in another direction (for example, from the transmitter 125 to the receiver 123).

[0027] Accordingly, with respect to terminal 103, optical path 111 may be called the outbound path, and optical path 121 may be called the inbound path. Optical path 111 may include one or more optical fibers 117-1 to 117-n and one or more optical amplifiers 119-1 to 119-n, the latter located within the corresponding repeaters 131-1 to 131-n. Similarly, optical path 121 may include one or more optical fibers 127-1 to 127-n and one or more optical amplifiers 129-1 to 129-n, the latter located within the corresponding repeaters 131-1 to 131-n. Optical fibers 117-1 to 117-n and 127-1 to 127-n may correspond to individual segments of a single optical fiber 117 and / or a single optical fiber 127, which can be formed by coupling amplifiers with optical fibers 117 and 127, as shown in Figure 1.

[0028] For example, one or more optical amplifiers 119-1 to 119-n and / or 129-1 to 129-n may be erbium-doped optical fiber amplifiers (EDFA) and / or any other optical amplifiers. Also, although the transmitters 113, 115 and receivers 123, 125 are shown as separate components, it can be understood that the transmitters 113 and / or receivers 123 may be housed together in a single housing and may form a transponder and / or transceiver at terminal 103. Similarly, the transmitters 115 and receivers 125 may also be housed together in a single housing and may form a transponder and / or transceiver at terminal 105.

[0029] As described above, an optical path pair (e.g., optical paths 111, 121) may be configured as a set of amplifier pairs 119-1~119-n and 129-1~129-n within repeaters 131-1~131-n, which are communicatively coupled to the repeater using optical fiber pairs 117 (e.g., using optical fibers 117-1~117-n) and 127 (e.g., using optical fibers 127-1~127-n), and optical fiber pairs 117 and 127 may be contained within an optical fiber cable together with other optical fibers and / or optical fiber pairs supporting additional path pairs. As shown above and in Figure 1, for example, each repeater 131-1~131-n may include at least one pair of corresponding amplifiers 119-1~119-n, 129-1~129-n for each path pair, and / or additional amplifiers for additional path pairs. As shown in Figure 1, for example, repeater 131-1 may include amplifiers 119-1 and 129-1.

[0030] The optical amplifiers 119-1 to 119-n and 129-1 to 129-n may include EDFA and / or other rare-earth doped optical fiber amplifiers, Raman amplifiers, and semiconductor optical amplifiers (SOA). Each repeater 131-1 to 131-n may further include corresponding coupling paths 133-1 to 133-n that can be communicatively coupled between optical paths 111 and 121. The terms “coupled” and / or “coupled” or “communicatively coupled” as used in this paper may broadly mean any connection, positive connection, coupling, link and / or positive link, direct and / or indirect and / or wired and / or wireless connection, etc., but it should be understood that this does not mean that the coupled components and / or elements are directly connected to each other.

[0031] It is understood that the first and second optical fibers providing corresponding transmission and return paths may be contained within a bidirectional optical fiber pair and / or form a bidirectional optical fiber pair. The optical fiber pair may be an independent DAS-dedicated optical fiber pair. In addition, or instead, it may be an optical fiber pair carrying a payload, thereby the wavelength of the DAS signal may be outside the payload channel wavelength so that the DAS signal does not interfere with the payload signal. It is understood that the "Nth set" of opposing 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 / or housed within the same corresponding repeaters 131-1 to 131-n.

[0032] Distributed acoustic sensing (DAS) is being realized to continuously detect spatial interference along long-distance transmission / sensing optical fibers in real time using telecommunications optical fibers as distributed sensors. However, to date, distributed sensing has been limited to optical fiber lengths within a typical sensing application range of approximately 50 km, although some research units are extending this to 150 km. Furthermore, in repeater-type DAS systems with erbium-doped optical fiber amplifiers (EDFAs), typically only the first optical fiber span adjacent to the DAS interrogator unit (IU) (e.g., DAS transmitter and receiver) can be sensed.

[0033] To sense multiple spans in a submarine network, typical systems generally utilize multiple DAS interrogator units with different wavelengths. The maximum sensing frequency (in a multispan sensing system) is determined by the sensing distance covered by a particular DAS interrogator unit (excluding preamble fiber spans, e.g., spans without loopback paths, e.g., spans extending from the transmitter / receiver component to the first repeater) and corresponds to the total distance between spans using the same optical filter wavelength. In such systems, preamble fiber spans are not included in the sensing distance calculation because Rayleigh backscatter from these spans is filtered out using filters of other wavelengths.

[0034] Furthermore, in some conventional relay systems, including EDFAs (i.e., including multiple EDFA repeaters located on the communication path as shown in Figure 1), only the first span adjacent to the DAS interrogator unit can be sensed, while other spans cannot. This is because isolators are used at the output, input, and / or both of the EDFA, so the Rayleigh signal does indeed return through the underwater EDFA. To sense any span after the EDFA, an optical loopback path is used to route the Rayleigh signal in the reverse direction.

[0035] Some systems use a high-loss loopback (HLLB) as the loopback path. Figure 2a shows an example of a repeater 200 coupled to a high-loss loopback (which may be coupled to system 100 shown in Figure 1). The repeater 200 may be located on an optical communication path, which may include a communication span for transmitting optical signals from west to east (it should be understood that the directions used here are for illustrative purposes only and do not mean to limit the subject in any way), a communication span for receiving reflected optical signals, and a communication span for receiving signals transmitted from east to west. The repeater may include an input 201 and an output 203 for transmitting signals from west to east (which may be reflected or transmitted from east to west), and an input 205 and an output 207 for transmitting signals from east to west (which may be reflected or transmitted from west to east).

[0036] Repeater 200 may further include an EDFA 206, a coupler 208 (e.g., a 10dB coupler), an optical attenuator (LBO) 210, and a fiber Bragg grating (FBG) 212 located on the transmitting side of Repeater 200. Repeater 200 may further include an EDFA 216, a coupler 218 (e.g., a 10dB coupler), an optical attenuator (LBO) 220, and a fiber Bragg grating (FBG) 222 located on the receiving side of Repeater 200. Coupler 208 can be communicatively coupled to coupler 218. This allows coupling of signals transmitted from east to west, and those signals reflected in response to signals transmitted from west to east, and vice versa, as indicated by the double arrows.

[0037] A signal transmitted from west to east is received at input 201 and amplified by EDFA 206. It can then be transmitted to output 203 (e.g., to the next optical fiber span and / or destination). This signal may be used for any signals reflected in response to a coupled signal transmitted from east to west, and these signals are transmitted from coupler 218 to coupler 208. Similarly, a signal transmitted from east to west is received at input 205 and amplified by EDFA 216, and then transmitted to output 207 (e.g., to the next optical fiber span and / or destination). This signal may be used for any signals reflected in response to a coupled signal transmitted from west to east, and can be transmitted from coupler 208 to coupler 218.

[0038] However, systems based on the HLLB Repeater 200 typically suffer very high losses. For reflection grids, the loss can be around 32 dB, and for Rayleigh backscatter signals, the loss can be around 54 dB.

[0039] To solve these problems, some systems use a repeater 230 as shown in Figure 2b. As shown in Figure 2b, the repeater 230 may similarly be located on an optical communication path, which may include a communication span for transmitting optical signals from west to east, a communication span for receiving reflected optical signals, and a communication span for receiving signals transmitted from east to west. The repeater 230 may include an input 231 and an output 233 for transmitting signals from west to east (which may be reflected or transmitted from east to west), and an input 235 and an output 237 for transmitting signals from east to west (which may be reflected or transmitted from west to east).

[0040] Repeater 230 may further include EDFA 232, filter 234, EDFA 236, coupler 238, and a circulator 239 located on the transmitting side of repeater 230. Repeater 230 may further include EDFA 242, filter 244, EDFA 246, coupler 248, and a circulator 249 located on the receiving side of repeater 230. The circulator 239 can be communicatively coupled to the output of EDFA 236 and the input of EDFA 232, and can further be communicatively coupled to coupler 248. Coupler 248 can be communicatively coupled to the output of EDFA 246. The circulator 249 can be communicatively coupled to the output of EDFA 246 and the input of EDFA 242, and can further be communicatively coupled to coupler 238. Coupler 238 can be communicatively coupled to the output of EDFA 236. Circulators 239 and 249 may be configured to redirect signals transmitted and received by repeater 230 in the optical communication path. EDFAs 232, 236, 242 and 246 may be configured to amplify transmitted and received signals being transmitted between the west and east sides of repeater 230. Filters 234 and 244 use wavelength filtering techniques to filter one or more signal wavelengths (e.g., λ) of the amplified signal. i , λ i ') may be configured to filter. By using multiple EDFAs and filters, the repeater 230 may be configured to enhance the signal power of the transmitted and / or reflected signals (e.g., enhance by 50 dB or more).

[0041] However, if the above system is used and acoustic frequency coverage is not lost, sensing multiple spans may be difficult. The acoustic frequency coverage of a single DAS interrogator unit is inversely proportional to the length of a particular sensing segment. For example, if a 10,000 km link is sensed using a single DAS interrogator unit, only acoustic frequencies below 5 Hz can be sensed. Some systems may divide the link into multiple segments, each of which may be covered by a different interrogator unit using a different wavelength. In this case, only the return of the wave from the corresponding DAS interrogator unit to the reverse path (e.g., as shown in Figure 2b) is permitted. Therefore, such a system may need to use optical bandpass filters in its loopback path (e.g., filters 234, 244 shown in Figure 2b), which may be specific to a particular interrogator unit and used to filter optical signals with different wavelengths.

[0042] For maximum acoustic sensing frequencies, each span may need to be covered by a single interrogator unit, and each loopback path may need to be different (for example, allowing the transmission of signals with wavelengths corresponding to interrogator units covering a particular span for transmitting reflected signals using different optical filters). This allows for maximum acoustic frequency coverage. Therefore, in an exemplary optical communication / sensing system with 200 optical communication spans, to obtain maximum acoustic frequency coverage, 200 individual interrogator units (each with a different wavelength) and 200 different loopback paths with different bandpass filters would be required. This has several drawbacks.

[0043] Firstly, a system with 200 interrogator units (each with a different wavelength) and 200 loopback passes (each with a different bandpass filter) would be extremely expensive and difficult to service and maintain, potentially requiring a large number of spare parts (e.g., interrogator units, filters, loopback passes, etc.) to ensure uninterrupted coverage. Furthermore, all 200 interrogator units require time synchronization, time interleaving, and cannot overlap in time. Otherwise, the nonlinearity between WDM DAS wavelengths would degrade the quality of the sensing signal and reduce sensing sensitivity.

[0044] Furthermore, the duty cycle of each DAS channel can be very low (for example, DAS pulses of all wavelengths cannot overlap in time). If 200 interrogator units are required, the maximum duty cycle may be less than 0.5%.

[0045] Furthermore, the power consumption of the interrogator units may be very low. The DAS wavelength covering the last span may need to propagate through all lead EDFAs, but it cannot be consumed for sensing only in the last span. The DAS wavelength covering the first span still consumes optical power in the downstream EDFA. If transmission of all DAS channels to the back of the communication link is permitted, and there are 200 interrogator units simultaneously on the link, the useful power for sensing each DAS channel may be as low as 0.5%. Power consumption may increase if a DAS channel that may have completed sensing drops out of the communication link. However, in this case, the sensing system may need to be carefully designed to reduce sensing sensitivity, as the remaining channel power may be too strong to generate nonlinearity.

[0046] Additionally, some DAS signals may fade. This can cause Rayleigh signals to weaken and / or disappear completely.

[0047] Furthermore, when using multiple DAS channels, it may be possible to perform only unidirectional sensing; otherwise, weak Rayleigh backscatter signals may be degraded by copropagated DAS signals transmitted along the reverse direction. Because unidirectional sensing requires one DAS channel to sense the entire span, its sensitivity is far lower compared to bidirectional sensing (sensing half the span). To maintain the same sensitivity, the number of repeaters needs to be doubled (half the span length), further increasing the system cost.

[0048] Furthermore, DAS signals are unlikely to coexist with signals transmitted on data communication channels. Because DAS sensing channels use very strong pulse power to perform pulse or OOK modulation, they can significantly reduce the performance of nearby data communication channels. In addition, the short pulses of DAS channels can cause undesirable EDFA transient effects.

[0049] To address the aforementioned problems of conventional systems, the current subject can be configured to perform multispan sensing using a single wavelength to cover long underwater optical communication links (e.g., longer than 10,000 km), and such links may include one or more identical repeaters without sacrificing the acoustic frequency range (e.g., greater than 1 kHz). The system of the current subject not only overcomes the aforementioned technical shortcomings of conventional systems but also offers greater cost-benefit for monitoring long underwater cables (including ship detection, fish / whale observation, earthquake / tsunami / landslide forecasting, etc.) using optical amplifiers.

[0050] In some embodiments, the system of the present subject comprises a sensing and interrogation unit (e.g., located at one end and / or each end of an optical sensing communication path) and one or more sensing units (e.g., repeaters) located at the sensing and interrogation unit and communicatively coupled to the sensing and interrogation unit using the optical communication path. The sensing units may be positioned at predetermined intervals, for example, equidistant from each other and / or at any desired distance from each other and / or at any desired distance from the sensing and interrogation unit. The sensing and interrogation unit may include a transmission optical device, for example, a laser (e.g., a scanning laser, a continuous-wave laser, a multi-tone frequency laser, and any combination thereof) configured to generate an optical signal (e.g., an interrogation signal) and transmit the optical signal to a plurality of sensing units, the optical signal may be a single-wavelength optical signal. The system may further include a receiving optical device that is communicatively coupled to the optical transmission path and configured to receive a plurality of reflected signals (e.g., optical signals that can be backscattered) in response to the optical signal.

[0051] A sensing and interrogation unit may be configured to transmit optical signals to multiple sensing units to determine the state of one or more portions (e.g., spans) of an optical communication path. Multiple reflected signals may also be received in response to such signal transmission. As discussed in this paper, reflected signals may be transformed in the frequency and time domains. For example, multiple reflected signals may be transformed in the frequency domain (e.g., using a windowed Fast Fourier Transform (FFT)) to determine one or more locations corresponding to approximate locations where signal reflections may occur in the optical communication path. The reflected signals (which may have already been transformed in the frequency domain) can then be transformed in the time domain (e.g., using an FFT) to determine one or more changes in the reflected signals over a given time period (e.g., determining what happened to the signal over time). These transformations contribute to determining the precise location of the reflected signals and can determine the state of the optical communication link (e.g., whether there is interference, interruption, seismic events, etc.).

[0052] In some embodiments, the interrogation and sensing unit may be configured to process reflected light signals continuously by processing portions of the signal being received in real time. For example, the interrogation and sensing unit may be configured to process a first set of reflected signals that can be received in a first time period (e.g., by transforming them in the frequency domain and time domain using a sliding window FFT), and to be able to process reflected signals received later (e.g., received in a second time period) while these signals are being processed. This allows for an increase in the acoustic range frequency.

[0053] To perform the determination of the state of the optical communication path, the interrogation and sensing unit may be configured to implement various processing techniques based on optical frequency domain reflectometry (OFDR) or frequency modulated continuous wave (FMCW). For example, as shown in curve 300 in Figure 3a, OFDR can be used to periodically modulate the frequency of a continuous wave (CW) laser of the interrogation and sensing unit having a narrow linewidth using a linear chirp. Modulation can be performed while the instantaneous amplitude and / or power are kept constant. In curve 300, line 301 can correspond to a chirp signal transmitted from the transmitter of the interrogation and sensing unit, and the same signal can also be used to serve a local oscillator (LO) in the receiver of the interrogation and sensing unit. The laser frequency can then be linearly modulated at Δf = γt, where γ is the frequency scan rate. In a receiver, heterodyne detection can typically be performed to beat the LO (Low-Level) by utilizing signals that can be backscattered from the communication span sensed in response to the signal transmitted from the transmitter. The distance of the optical fiber segment to the interrogation and sensing units can be proportional to the beat frequency.

[0054] Figure 3b shows a curve 310 illustrating the relationship between beat frequencies (e.g., Δf1~Δf4) and time in the receiver. Frequency Δf0=0 can correspond to the Rayleigh backscatter signal from the start of the communication link (e.g., position in the first span between the interrogation and sensing unit and the first repeater). Frequencies Δf1~Δf4 can correspond to the Rayleigh backscatter signal that can be reflected by the corresponding positions L1~L4 (e.g., as shown in plot 303 in Figure 3a, L1 may be the length of the sensing span, and the reflected signal may be the one reflected by position z1 at time t1; as shown in plot 305 in Figure 3a, L2 may be the length of another sensing span, and the reflected signal may be the one reflected by position z2 at time t2, etc.). Typically, the beat frequency Δf between any position z (e.g., z1, z2 as shown in Figure 3a) away from the interrogation and sensing unit and the sensing signal reflected by LO and position z is... z The relationship between them can be expressed as follows:

[0055]

number

[0056] OFDR spatial resolution (SR) L SR This can be expressed as follows:

[0057]

number

[0058] The receiver bandwidth is Δf, not ΔF as shown in Figure 3a (where L is the length of the sensing link). LThis can be confirmed by =γ·2nL / c. Because the spatial resolution of OFDR is inversely proportional to the chirp ΔF, very fine spatial resolution can be achieved. Some OFDR systems perform sensing with a spatial resolution of μm~cm and may have short sensing distances (e.g., the level of integrated devices is a few meters) to avoid processing large amounts of data.

[0059] In some embodiments, the present subject may be configured to use OFDR technology and process the reflected optical signal using a windowed Fast Fourier Transform (FFT) method to achieve acoustic sensing where the Nyquist frequency of a 1 mm optical communication link is greater than 1 kHz. In addition, or alternatively, the present subject may be configured to use OFDR technology and process the reflected signal using a sliding window FFT method to achieve a Nyquist frequency of greater than 10 kHz for a 1 mm optical link. Neither of these methods sacrifices acoustic frequency range and can be used to perform multispan sensing using a single wavelength to cover, for example, long-distance underwater optical communication links longer than 10,000 km (which may include all the same repeaters).

[0060] Figure 4a shows an exemplary optical communication system 400 according to several embodiments of the present subject, which can be used to perform state determination of one or more portions (e.g., spans) of an optical communication path. Figure 4b shows an example of the signal flow of a data channel in the optical communication system 400 according to several embodiments of the present subject. Figure 4c shows an example of the signal flow of a DAS channel in the optical communication system 400 according to several embodiments of the present subject.

[0061] System 400 can be used in underwater / seabed and / or terrestrial environments. In particular, System 400 can be used in interrogation and / or sensing (including DAS) environments and is used to monitor the span and / or sections of one or more optical paths and / or links that may not be directly and communicatively coupled to interrogation and sensing units.

[0062] In some embodiments, during operation, to monitor a sensing span including one or more optical paths and / or portions thereof, the transmitter of the interrogation and sensing unit may be configured to generate an optical sensing signal (e.g., an interrogation pulse) that can be transmitted toward the monitored optical path. As discussed in this paper, the optical sensing signal may be configured to be transmitted via various optical devices (e.g., including one or more circulators, couplers, amplifiers, filters and / or any other types of optical devices, and / or any combination thereof). The pulse can be transmitted toward one or more repeaters toward the optical path to reach sections and / or entire optical paths that may need to be monitored.

[0063] In response to receiving an interrogation pulse from the transmitter of the interrogation and sensing unit, the sensing span may be configured to reflect and / or backscatter the optical sensing signal along the entire length of the sensing span. The reflected / backscattered signal may be configured to be sent back toward the receiver of the interrogation and transmitting unit. In particular, the reflected / backscattered signal can be transmitted through various optical paths, which may include one or more optical devices (e.g., circulators, couplers, amplifiers, filters and / or one or more of any other optical devices and / or any combination thereof). The interrogation and sensing unit may be configured to perform an analysis of the received signal to determine whether there is any interference, interruption, etc. in the optical path based on disturbances in the backscattered signal, and to determine the specific location of such interference, interruption, etc. The analysis may be performed using one or more processing components of the interrogation and sensing unit, and may also involve the use of optical frequency domain reflection (OFDR) techniques. This may include collecting one or more data points related to backscattered / reflected signals, performing transformations on such points in the frequency and time domains (e.g., using the Fast Fourier Transform (FFT)), and determining the specific locations of interferences, interruptions, etc.

[0064] In some embodiments, the system 400 may be configured to allow copropagation of signals in the data channel and the sensing channel. However, it is understood that data and sensing signals may be transmitted on separate channels. The system may be configured to include terminals (east and west, as shown in Figure 4a), which may be configured to perform OFDR techniques to analyze the communication spans that may be located near the output of each repeater in that direction (e.g., a terminal can monitor half of the span (e.g., in the east or west direction) and / or the entire span (e.g., in both directions)). Each repeater may include two loopback paths, each loopback path having an EDFA and an optical filter (which may be based on a specific wavelength). The EDFA can be used to enhance weak Rayleigh signals (e.g., signals reflected in response to sensing signals), and the optical filter can filter out WDM data channels copropagating in one direction to avoid affecting the data channel from the opposite direction. In a forward path, a loopback path and a backward path can be linked using a circulator and a coupler.

[0065] Furthermore, in some exemplary, non-limiting embodiments, if the span length is less than 50 km and / or sensing sensitivity is not an issue, system 400 may be configured to use only a single wavelength. Also, if, for example, only the west-to-east direction needs to be sensed, all components in the repeater in the reverse loopback direction (e.g., circulator, EDFA, filter, coupler, etc.) can be removed and / or kept inactive. System 400 can have the advantages of various technologies. System 400 may be configured to have a full (e.g., 100%) duty cycle and to use full (100%) OFDR power in the interrogation and sensing units. The use of full duty cycle and full power in the OFDR channels may result in much higher sensitivity for system 400 than for conventional systems, and it simplifies the return path and reduces costs. Also, a single interrogation and sensing unit may suffice (e.g., one on each side for longer spans and higher sensitivity). Furthermore, due to the frequency diversity characteristics of OFDR technology, system 400 may have minimal fading. Moreover, it can provide bidirectional sensing with no loss of sensitivity and / or error. System 400 can copropage with the data channel, have little to no impact on the data channel, and / or have no impact on the data channel, and / or originate from the data channel. Finally, system 400 may be configured to virtually eliminate transient effects in EDFA.

[0066] Referring to Figure 4a, the system 400 may include terminals 402 and 420, which can be communicatively coupled using one or more optical communication paths 401, 491, at least some of which may be located underwater and / or on the seabed. As a non-limiting example, path 401 may communicatively couple terminal 402 to terminal 420 for transmitting signals in a west-to-east direction, and path 491 may communicatively couple terminal 420 to terminal 402 for transmitting signals in an east-to-west direction. Path 401 may include one or more spans 410(a, b, c), and similarly, path 491 may include one or more spans 412(a, b, c). It should be understood that providing the indicated direction and / or use of paths 401, 491 is explanatory, not limiting. Also, any number of spans may exist.

[0067] The western terminal 402 may include an interrogation and sensing unit 403, which may include a sensing signal source (e.g., a CW laser) for transmitting a sensing optical signal (e.g., having a single wavelength λ1) toward terminal 420, a data source 405 for transmitting data over one or more optical data paths, a wavelength division multiplexing (WDM) component 409, an EDFA 411, a circulator 413, an EDFA 415, a bandpass filter 417, a coupler 421, and an EDFA 419. The interrogation and sensing unit 403 can be communicatively coupled to a circulator 407, which can route optical signals from the interrogation and sensing unit 403 (e.g., a data channel from data source 405 and a sensing signal having wavelength λ1) and optical signals from EDFA 419 (e.g., a Rayleigh reflection signal at λ1 and a data channel from data source 425 at terminal 420). Circulator 407 can be communicatively coupled to WDM component 409, which can be used to process optical and data signals, the latter originating from data source 405. Once the signals are processed by WDM component 409, EDFA 411 may be configured to amplify them for transmission along optical path 491 toward terminal 420 via circulator 413. In addition, or alternatively, sensing signals reflected by Rayleigh can be routed from circulator 413 to EDFA 415 for amplification. The amplified signals can then be filtered using filter 417 (e.g., λ1 bandpass filter) and routed to coupler 421, which can combine them with signals received in optical communication path 401 (Rayleigh reflected signals at λ1 and data channels from data source 425 at terminal 420). The combined signals can then be provided to EDFA 419 for further amplification.

[0068] Similarly, the eastern terminal 420 may include an interrogation and sensing unit 423, which may include a sensing signal source (e.g., a CW laser) for transmitting a sensing optical signal (e.g., having wavelength λ2) toward terminal 402, a data source 425 for transmitting data over one or more optical data paths, a WDM component 429, an EDFA 431, a circulator 433, an EDFA 435, a bandpass filter 437, a coupler 441, and an EDFA 439. The interrogation and sensing unit 423 can be communicatively coupled to the circulator 427 to route optical signals from the unit 423 (e.g., a data channel from the data source 425 and a sensing signal having wavelength λ2) and optical signals from the EDFA 439 (e.g., a Rayleigh reflection signal at λ2 and a data channel from the data source 405 at terminal 402). The circulator 427 can be communicatively coupled to a WDM component 429, which can process optical and data signals. The WDM component 429 can route the signals to an EDFA 431 for amplification and then transmit them along the optical path 401 toward the terminal 402 via the circulator 433. In addition, or alternatively, the Rayleigh reflected signal from the span 410c signal can be routed by the circulator 433 to an EDFA 435, which can then be filtered using a filter 437 (e.g., a λ2 bandpass filter). The filtered signal can then be routed to a coupler 441, which can combine them with signals received in the optical communication path 491 (the Rayleigh reflected signal at λ2 and the data channel from the data source 405 at the terminal 402). The combined signal can then be provided to the EDFA 439 for amplification.

[0069] The system 400 may include one or more repeater components 404(a, b). Although only two repeaters 404 are shown in Figure 4a, it can be understood that the system 400 may include any number of repeaters as needed. The repeaters 404 can be communicatively coupled to optical paths 401 and 491 using corresponding optical communication spans 410(a, b, c) and 412(a, b, c), and may be located underwater / on the seabed between terminals 402 and 420. For example, terminal 402 can be communicatively coupled to repeater 404a using an east-to-west optical communication span 410a and a west-to-east optical communication span 412a. Similarly, repeater 404a can be communicatively coupled to repeater 404b using the east-to-west optical communication span 410b and the west-to-east optical communication span 412b, and repeater 404b can be communicatively coupled to terminal 420 using the east-to-west optical communication span 410c and the west-to-east optical communication span 412c.

[0070] As described above, the repeater 404 may be located on optical communication paths 401 and 491 for transmitting (e.g., sending and receiving) optical signals from west to east (e.g., path 401) and for transmitting (e.g., sending and receiving) optical signals from east to west (e.g., path 491). As shown in Figure 4a, the repeater 404a may be commutably coupled to span 412a to receive signals transmitted from west to east, and may be commutably coupled to span 410a to output signals transmitted from east to west. Furthermore, it may be coupled to span 412b to output signals processed by the repeater 404a, and may be coupled to span 410b to receive signals transmitted from east to west.

[0071] The repeater 404a may include a coupler 451a, an EDFA 449a, and a circulator 463a, and may be configured to process signals received through span 412a (e.g., a data channel from data source 405 and a signal having wavelengths λ1 and λ2) and output them to span 412b, where the Rayleigh reflected signals from span 412b are routed through the circulator 463a to an EDFA 465a (e.g., for amplification) and a filter 467a (e.g., a filter based on λ1). The signals filtered by filter 467a can be provided to a coupler 471a, which can couple them with signals received from span 410b (e.g., a data channel from data source 425 and a sensing signal having wavelengths λ1 and λ2). The coupler 471a may be commutably coupled to an EDFA 469a, which may further be coupled to a circulator 443a. The circulator 443a can transmit signals to span 410a (e.g., data channel, λ2 sensing signal from loopback, and λ1 sensing signal) and / or simultaneously route Rayleigh reflected signals from span 410a to EDFA 445a and filter 437a (e.g., λ2-based filter).

[0072] As described above, circulators 443a and 463a may be configured to redirect signals transmitted and received by repeater 404a on optical communication paths 401 and / or 491, and EDFAs 445a, 449a, 465a and 469a may be configured to amplify Rayleigh reflected signals from the loopback and transmitted and received signals (and vice versa) transmitted between the west and east sides of repeater 404a. Filters 437a and 467a may be configured to filter one of the sensing wavelengths (e.g., λ1, λ2) by applying wavelength filtering techniques. Thus, with multiple EDFAs and filters, repeater 404a may be configured to enhance the signal power of transmitted and / or reflected signals. The structure and / or operation of repeater 404b (and / or any other repeaters available in system 400) may be similar to the structure and / or operation of repeater 404a. However, it can be understood that each repeater located on communication paths 401 and 491 may be similar to and / or different from another repeater. The structure and / or operation of each repeater may be determined based on the specific requirements and / or design of the optical communication system.

[0073] Referring to Figure 4b, as described in this paper, the optical communication system 400 may be configured to transmit one or more data signals from one or more data sources 405 and 425 via one or more data channels. For example, a data signal from data source 405 can be transmitted from west to east to data source 425 via data channel 482 (as shown by the dashed line in Figure 4b). Similarly, a data signal from data source 425 can be transmitted from east to west to data source 405 via data channel 481 (as shown by the solid line in Figure 4b). Data channels 482 and 481 may be separate from and / or part of optical communication paths 491 and 401, respectively. In some embodiments, a filter 417 can be used to remove data signals 484 (e.g., reflected Rayleigh signals from optical fibers) transmitted from circulator 413 through EDFA 415 at terminal 402, thereby reducing the penalty for signal 481. Similarly, repeater 404 can filter such data signals using the corresponding filter 467. Likewise, filter 437 can be used to remove data signals 483 (e.g., reflected Rayleigh signals from optical fibers) transmitted from circulator 433 through EDFA 43 at terminal 420, thereby reducing the penalty to signal 482. Similarly, repeater 404 can filter data signals in a similar manner using the corresponding filter 437.

[0074] Referring to Figure 4c, as described in this paper, the optical communication system 400 can be used to send and receive one or more sensing signals (e.g., DAS signals) between terminals 402 and 420. One or more sensing signals can be sent and received using optical communication paths 401 and / or 491. The interrogation and sensing unit 403 of terminal 402 may be configured to transmit one or more sensing signals toward terminal 420 via one or more repeaters 404 using wavelength λ1. The transmission path of such signals is shown by a dashed line. Any signal having the same wavelength λ1 that can be reflected can be transmitted toward terminal 402 via one or more repeaters 404. The transmission path of such reflected signals is similarly shown by a dashed line in Figure 4c. Similarly, the interrogation and sensing unit 423 of terminal 420 can transmit a sensing signal toward terminal 402 in a westward direction using wavelength λ2. The transmission path of such westward sensing signals is shown by a solid line. Reflected signals of the same wavelength can be transmitted toward the terminal 420 via one or more repeaters 404 (as shown by the solid lines in Figure 4c).

[0075] Although EDFA is shown as the amplifier implemented by system 400, any other type of amplifier may be used, such as a rare-earth doped optical fiber amplifier, a Raman amplifier, or a semiconductor optical amplifier (SOA). Furthermore, the amplifiers may be similar to each other and / or different from one component (e.g., terminals 402, 420, repeater 404, etc.) to another component.

[0076] Figures 9a-9c show various embodiments of repeaters that can be implemented in system 400. Figure 9a shows repeater 902, similar to repeater 404(a,b) shown in Figure 4a, and the repeater can use loopback amplification and bandpass filtering. Figure 9b shows exemplary repeater 904, similar to repeater 902 but without using an EDFA between the filter and circulator. This repeater can be used in small systems. Repeater 906 can provide bandpass filtering to remove reflected data channels. Figure 9c shows exemplary repeater 906, similar to repeaters 902 and 904 but without using a loopback EDFA and filter. Repeater 906 can provide simple loopback processing and can be used in even smaller systems. It can be understood that any type of repeater may be used.

[0077] Figure 10 shows another installation of repeater 1002 available in system 400. Repeater 1002 may be similar to repeater 404, with EDFAs 1004 and 1006 correspondingly positioned before couplers 471a and 451a. Repeater 1002 may be configured as an out-to-out repeater, and the repeaters shown in Figures 4a and 9a-c may be configured as out-to-in repeaters. Similar to the embodiments shown in Figures 9b-c, repeater 1002 may be further modified to remove various components such as one or more loopback filters 437a, 467a and / or one or more loopback EDFAs 445a, 465a.

[0078] The following illustrates exemplary OFDR-based processing performed by one or more terminals 402, 420 with reference to the discussion in Figures 5-8. Specifically, the interrogation and sensing unit (e.g., unit 403 of terminal 402) may be configured to include processing components and / or systems (e.g., the processing components or systems shown in Figure 12) capable of performing such OFDR-based processing. Figures 5-6b show signal processing based on a windowed OFDR performed by system 400, and Figures 7a-78 show signal processing based on a sliding window OFDR performed by system 400.

[0079] In some systems, after a full frequency scan and beat frequency unit, an interrogation unit (e.g., a DAS interrogation unit) can digitize the signal using its analog-to-digital converter (ADC) as defined in equation (2) above, apply a Fast Fourier Transform (FFT) to the full scan data, and generate an acoustic response with spatial resolution (SR). By repeating the frequency scan, periodic disturbance signals can be recovered if the frequency of the disturbance signal is less than half the repetition rate of the chirp scan. In some cases, the OFDR scan period may be at least twice the time of flight of the link. Thus, for a 10,000 km optical communication link, the round-trip time may be approximately 100 milliseconds (ms), generating a chirp repetition rate of less than 10 Hz and a maximum detected acoustic frequency of less than 5 Hz.

[0080] In some embodiments, the current subject (e.g., system 400) may be configured to increase the acoustic frequency detection range using the windowed FFT technique shown in Figure 5. As a non-limiting example, for a 10,000 km link with a spatial resolution of 200 m, system 400 may be configured to include 50,000 "sensors". To cover an acoustic frequency range of 1 kHz, the interrogation rate (IR) of the interrogation and sensing unit 403 (and / or unit 423) may be at least 2 kHz. Thus, unit 403 may be configured to produce a total throughput of 200 MS / s. In addition, or instead, unit 403 (and / or terminal 402) may include an ADC having a throughput greater than 200 MS / s.

[0081] Referring to Figure 5, and using the above example (i.e., a 10,000 km, 50,000 sensor optical communication links), the interrogation and sensing unit 403 (and / or 423) of system 400 may be configured to acquire the first 100,000 data points. To analyze the 50,000 sensors, twice the number of sampling points may be required, based on the Nyquist sampling theorem (which shows that an analog signal can be digitized without aliasing error only if the sampling rate is at least twice the highest frequency component in a given signal). Subsequently, unit 403 may convert the horizontal time-domain data 501 (e.g., 100,000 data points represented by solid circles 502 as shown in Figure 5 (similar to points represented by rhombuses 504, triangles 506, and plus signs 508)) to vertical frequency data 503 (e.g., 2 x 50,000 data points, one pair for each sensed location). This is given by nFFT1 = 2L ink / L SRIt can be realized by determining the FFT of 501 points of 100,000 time-domain data at 100k and obtaining 100,000 frequency points 503. One positive frequency data point and one negative frequency data point correspond to the position of each sensor (for example, as shown in Fig. 3b). Subsequently, the interrogation and sensing unit 403 can determine the sum of the powers of the optical signals from the same position (for example, one is at the positive frequency and one is at the negative frequency) (for example, generating 50,000 vertical data points). Unit 403 can repeat these operations 2000 times to generate a 50000x2000 matrix 503.

[0082] Subsequently, unit 403 rearranges the data and determines 50,000 FFTs at nFFT2 = 2k = 2f Nyquist and each FFT has 2000 points. The result of this determination can correspond to 2000 equivalent acoustic sampling points (for example, a total of 50,000) 505 at each sensed position. In some exemplary embodiments, for example, when frequency domain information is required, this operation is optional.

[0083] The interrogation and sensing unit 403 (and / or 423) can perform the above operations multiple times as needed to continuously monitor a 10000 km link with a spatial resolution of 200 m and an acoustic frequency range of 1 kHz. Also, when unit 403 and / or terminal 402 use an ADC with a higher sampling rate (for example, R ADC = 1 GS / s), the high data rate can be downsampled after averaging. The number of average values can be determined by the following formula. [[ID={13]]

[0084]

Equation

[0085] It should be understood that the above examples are for illustrative purposes only and not intended to limit the subject matter of this application. Optical communication links of any length can be monitored using any required spatial resolution and / or any required acoustic frequency range.

[0086] Figure 6a shows an exemplary process 600 for performing a windowed FFT by an interrogation and sensing unit 403 and / or terminal 402 according to several embodiments of the present subject. At 602, unit 403 can initiate a frequency scan and at 604 acquire an average of nAve data points. At 606, unit 403 can then perform data preprocessing (e.g., forming a serial data stream from dual-polarization (pol) IQ data or single-polarization data, filtering it to remove noise, etc.).

[0087] At 608, the interrogation and sensing unit 403 determines whether one or more moving averages need to be determined, and at 610 whether the first transformation (FFT1) needs to be determined. If it does not need to be determined, at 604 multiple points can be obtained. Otherwise, at 612, as described in this paper, nFFT1=2L ink / L SRThe transformation can be achieved by determining the FFT of 501 time-domain data points and obtaining frequency points 503, where one positive frequency data point and one negative frequency data point correspond to each sensed position. At 614, unit 403 can check whether the frequency scan is complete. If not, at 602, additional data points can be obtained. At 616, unit 403 can determine whether a second transformation needs to be determined. If not, at 604, multiple points can be obtained. Otherwise, at 618, the time-domain transformation can be performed. This is nFFT2=2f Nyquist This can be achieved by using, which may lead to one or more equivalent interrogation rates for each sensed location. In 620, unit 403 can perform data post-processing (e.g., extracting phase information from FFT data and performing further phase processing). Note that the equivalent interrogation period may differ from the chirp repetition rate. For example, system 400 can be designed to have one chirp repetition rate that covers multiple equivalent interrogation periods. If the interrogation period is longer than the chirp repetition rate, it is necessary to switch the order of some blocks (e.g., including the second FFT), as shown in Figure 6b.

[0088] Figure 6b shows another exemplary process 630 for performing a windowed FFT by the interrogation and sensing unit 403 and / or terminal 402 according to some embodiments of the present subject. Process 630 is similar to process 600 shown in Figure 6, performing the same sequence of operations until operation 612. Then, at 644 (similar to operation 616 in Figure 6a), unit 403 performs a determination of whether or not a second transformation needs to be performed. If not, the process returns to 604 to acquire multiple data points. Otherwise, at 646, the second transformation (i.e., time-domain transformation) can be performed (this operation is similar to operation 616 shown in Figure 6a). At 648 (similar to operation 614 in Figure 6a), unit 403 can determine whether or not the scan is complete, and if not, unit 403 can return to 604 to acquire further data points. Otherwise, post-processing (similar to operation 620 in Figure 6a) can be performed at 650.

[0089] As described above, Figures 7a-b and 8 show a sliding window FFT operation, which may be performed by system 400 to increase the acoustic frequency range.

[0090] Using the above windowed configuration, the maximum equivalent interrogation rate can be determined by the following formula.

[0091]

number

[0092] To achieve a higher interrogation rate, the ADC sampling rate R of unit 403 ADC This can be increased accordingly. Therefore, the interrogation and sensing unit 403 may be configured to perform a sliding window technique, which has a relatively low R ADCThis allows for a higher interrogation rate. Unit 403 uses the FFT non-overlap rate as noR FFT (0,1) can be defined as, however, noR FFT =1 is used for the windowed process discussed in relation to Figures 5-6b above, and in addition, or instead, if FFT window overlap is not defined, noR FFT = 0. FFT If is 0.5, unit 403 can double the acoustic frequency response by doubling the FFT result for the same number of time-domain data. Using the example discussed with respect to Figure 5 above (i.e., a 10,000 km link with a spatial resolution of 200 m and a throughput ADC of 200 MS / s), unit 403 may be configured to cover an acoustic frequency range of 10 kHz and / or an equivalent interrogation rate of 20 kHz. Since the Nyquist frequency is 1 kHz, unit 403 may need to perform oversampling of 10 times or more, or noR FFT = 0.1.

[0093] Referring to Figure 7a and using the above example, the interrogation and sensing unit 403 (and / or 423) may be configured to perform an FFT process with a sliding window. First, unit 403 can acquire the first 100,000 data points and set the start data pointer to 0.

[0094] Next, unit 403 may convert the horizontal time-domain data 701 (for example, 100,000 data points represented by solid circles 702 as shown in Figure 7a (similar to points represented by diamonds 704, triangles 706, and plus signs 708)) into vertical frequency data 703 (for example, 100,000 data points, one pair for each sensed position). This is done using nFFT1=2L ink / L SRThis can be achieved by determining the FFT of 701 time-domain data points at 100k and acquiring 100,000 frequency points 703, where one positive frequency data point and one negative frequency data point correspond to each sensor location (for example, shown in Figure 3b). Subsequently, the interrogation and sensing unit 403 can determine the sum of the power of the optical signals from the same location (for example, one at a positive frequency and one at a negative frequency) (for example, generating 50,000 vertical data points).

[0095] Subsequently, unit 403 can acquire another 10,000 data points (1 / 10 of the initial 100,000 data points) 711 and advance the data pointer by 10,000 (for example, from 10,000 to 110,000). Then, unit 403 can perform the above transformation operation using the data acquired from 10,000 to 110,000. These operations can be repeated 20,000 times to generate a 50,000 x 20,000 matrix 703.

[0096] Subsequently, unit 403 rearranges the data to separate the results of each row (originating from the same position) and can determine the response of system 400 based only on the newly added data point (for example, point 711 shown in Figure 7a). Then, unit 403 calculates nFFT2=20k=20f Nyquist Using this method, 50,000 FFTs can be determined, with each FFT containing 20,000 points. As shown in Figure 7b, the results of this determination can correspond to 20,000 equivalent acoustic sampling points (e.g., 50,000 in total) at each sensed location.505 In some exemplary embodiments, for example, if frequency domain information is required, this operation is optional.

[0097] Interrogation and sensing units 403 (and / or 423) can perform the above operations multiple times as needed to continuously monitor a 10,000 km link with a spatial resolution of 200 m and an acoustic frequency range of 10 kHz. Furthermore, units 403 and / or terminal 402 can perform the above operations multiple times as needed to achieve higher sampling rates (e.g., R ADC When using an ADC with a averaging rate of 1 GS / s, high data rates can be downsampled after averaging. The number of averages can be determined by the following formula.

[0098]

number

[0099] Figure 8 shows an exemplary process 800 for performing a sliding window FFT by an interrogation and sensing unit 403 and / or terminal 402 according to several embodiments of the present subject. In 802, unit 403 may be configured to invoke start and end FFT pointers (e.g., psFFT - FFT start pointer and peFFT - FFT end pointer). These pointers can be used to control the FFT1 process, where peFFT++ can be equivalent to peFFT = peFFT + 1, and psFFT += nFFT1 * noR FFT psFFT = psFFT + nFFT1 * noR FFT It can be equivalent to this.

[0100] Subsequently, at 804, unit 403 can initiate a frequency scan and acquire an average of nAve data points at 806. Then, at 808, unit 403 can perform data preprocessing (e.g., forming a serial data stream from dual-polarization (pol) IQ data or single-polarization data, and filtering to remove noise).

[0101] At 810, unit 403 can determine one or more moving averages, and at 812, it can determine peFFT++ using the above relationship. At 814, unit 403 can determine whether it may be necessary to perform a first transformation, i.e., whether peFFT-psFFT=nFFT1. If it is not necessary, at 806, multiple points can be obtained. Otherwise, as described in this paper, at 816, unit 403 can perform a frequency transformation, i.e., nFFT1=2L link / L SR By using this, the FFT of 701 time-domain data points can be determined, and frequency points 703 corresponding to each sensed position can be obtained. At 818, unit 403 can increase psFFT by nFFT1*noRFFT, and at 820, it can determine whether a second transformation may need to be performed. If not, at 806, additional data points can be obtained. Otherwise, at 822, the time-domain transformation can be determined, and at 824, a check can be performed to see if the frequency scan is complete. If not, at 806, additional data points can be obtained.

[0102] Figure 11 shows an exemplary process 1100 for monitoring an optical transmission path in an optical transmission system according to several embodiments of the present subject. Method 1100 can be performed by interrogation and sensing units 403 and / or 423 and / or terminals 402 and / or 420 (for example, in system 400 shown in Figure 4a).

[0103] In 1102, unit 403 can transmit an optical signal to multiple sensing units to determine the state of one or more parts of an optical communication path, and in 1104, it can receive multiple reflected signals in response to the optical signal. Then, in 1106, unit 403 can perform one or more transformations of the multiple reflected signals in at least one of the frequency domain and time domain (as discussed in Figures 5-8). In 1108, unit 403 can determine the state of one or more parts using the transformed multiple reflected signals. Unit 403 can perform process 1100 by implementing one or more processing systems and / or components. An example of such a processing system is shown in Figure 12.

[0104] As shown in Figure 12, the processing system 1200 may include an input / output (I / O) device 1201, a processor 1203, a memory 1205, storage 1207, and one or more communication components 1211. Each of the components 1201 to 1207 can be connected to one another by a system bus 1209. The processor 1203 may be configured to process instructions for execution within the system 1200. In some embodiments, the processor 1203 may be a single-threaded processor. In addition, or instead, the processor 1203 may be a multi-threaded processor. The processor 1203 may be configured to process instructions stored in the memory 1205 and / or storage 1207, including, but not limited to, receiving and / or transmitting information by the I / O device 1201. The memory 1205 can store information within the system 1200. In some embodiments, the memory 1205 may be a computer-readable medium. In addition, or instead, the memory 1205 may be a volatile memory unit. In some embodiments, memory 1205 may be a non-volatile memory unit. Storage 1207 can provide mass storage to system 1200. In some embodiments, storage 1207 may be a computer-readable medium. In addition, or alternatively, storage 1207 may be a floppy disk device, a hard disk device, an optical disk device, a tape device, a non-volatile solid memory, or any other type of storage device. I / O device 1201 can provide input / output operations to system 1200. In some embodiments, I / O device 1201 may include a keyboard and / or a pointing device. In addition, or alternatively, I / O device 1201 may include a display unit for displaying a graphical user interface.

[0105] In some exemplary embodiments, one or more components of System 1200 may include any combination of hardware and / or software. In some embodiments, one or more components of System 1200 may be located on one or more computing devices, such as one or more servers, one or more databases, one or more personal computers, one or more laptop computers, one or more mobile phones, one or more smartphones, one or more tablet computers, virtual reality devices and / or any other computing devices and / or any combination thereof. In some exemplary embodiments, one or more components of System 1200 may be located on a single computing device and / or as components of a single communication network. In addition, or instead, such services may be located separately from one another.

[0106] In some embodiments, one or more components of System 1200 may include a network-supporting computer. As described in this paper, the network-supporting computer may include, but is not limited to, computer devices or communication devices, such as servers, network devices, personal computers, workstations, telephones, smartphones, handheld PCs, personal digital assistants, thin clients, fat clients, internet browsers, or other devices. One or more components of System 1200 may be mobile computing devices such as Apple's iPhone®, iPod®, iPad®, and / or any other suitable device running Apple's iOS® operating system, or any device running Microsoft's Windows®. Mobile operating systems, any device running Google's Android® operating system, and / or any other suitable mobile computing devices are, for example, smartphones, tablet computers, or similar wearable mobile devices.

[0107] One or more components of System 1200 may include a processor and memory, and the processing circuit may include additional components necessary to perform the functions described herein, including the processor, memory, error and parity check / CRC tester, data encoder, collision avoidance algorithm, controller, command decoder, security primitives, and tamper-proof hardware. One or more components of System 1200 may further include one or more displays and / or one or more input devices. The displays may be any type of device that displays visual information (e.g., computer monitors, flat panel displays, and mobile device screens), and include liquid crystal displays, light-emitting diode displays, plasma panels, and cathode ray tube displays. The input devices may include any devices for inputting information into a user device, which are available to and supported by the user device, and include, for example, a touchscreen, keyboard, mouse, cursor control device, touchscreen, microphone, digital camera, video camera, or portable camera. These devices can be used to input information and interact with the software and other devices described herein.

[0108] In some exemplary embodiments, one or more components of the system 1200 may run one or more applications (e.g., software applications) which may, for example, communicate with one or more components of the system 1200 over a network to send and receive data.

[0109] One or more components of system 1200 may include one or more servers and / or be able to communicate with one or more servers via one or more networks and operate as a front-end-back-end pair corresponding to one or more servers. One or more components of system 1200 may transmit one or more requests to one or more servers from, for example, a mobile device application (e.g., running on one or more user devices, components, etc.). These requests may relate to retrieving data from the servers. The servers may receive requests from the components of system 1200. In response to these requests, the servers may be configured to retrieve the requested data from one or more databases. Based on receiving the requested data from the databases, the servers may be configured to transmit the received data to one or more components of system 1200, and the received data may respond to one or more requests.

[0110] System 1200 may include one or more networks and / or be communicatively coupled to one or more networks. In some embodiments, the networks may be one or more wireless networks, wired networks, or any combination of wireless and wired networks, and may be configured to connect to components of System 1200 and / or to connect components of System 1200 to one or more servers. For example, a network may include one or more of the following types of networks and / or any other combination thereof: fiber optic networks, passive optical networks, cable networks, the Internet, satellite networks, wireless local area networks (LANs), metropolitan area networks (MANs), wide area networks (WANs), virtual local area networks (VLANs), extranets, intranets, global mobile communication systems, personal communication services, personal area networks, wireless application protocols, multimedia messaging services, enhanced messaging services, short message services, time division multiplexing systems, code division multiplexing access systems, D-AMPS, Wi-Fi®, fixed wireless data, IEEE 802.11b, 802.15.1, 802.11n and 802.11g, Bluetooth, NFC, radio frequency identification (RFID), Wi-Fi® and / or any other type of network.

[0111] Furthermore, the network may include, but is not limited to, telephone lines, optical fibers, IEEE Ethernet® 802.3, wide area networks, wireless personal area networks, LANs, or global networks such as the Internet. The network may also support the Internet, wireless communication networks, cellular networks, etc., or any combination thereof. The network may further include one network, or any number of the exemplary types of networks described above, operating as independent networks or in conjunction with one another. The network may utilize one or more protocols of one or more network elements that are communicatively coupled. The network may convert to one or more protocols of network devices, or convert from other protocols to one or more protocols of network devices. The network may include multiple interconnected networks such as the Internet, service provider networks, cable television networks, company networks, and home networks.

[0112] System 1200 may include one or more servers and / or be communicatively coupled to one or more servers, the servers of which may include one or more processors that can be coupled to memory. The servers may be configured as a central system, server, or platform to control and retrieve various data at different times to perform multiple workflow operations. The servers may be configured to connect to one or more databases. The servers may be incorporated into at least one component of System 1200 and / or be communicatively coupled to that component.

[0113] The various elements of the component described with reference to Figures 1 to 12 above may include various hardware elements, software elements, or combinations thereof. Examples of hardware elements may include devices, logic devices, components, processors, microprocessors, circuits, processors, circuit elements (e.g., transistors, resistors, capacitors, inductors, etc.), integrated circuits, application-specific integrated circuits (ASICs), programmable logic devices (PLDs), digital signal processors (DSPs), field programmable gate arrays (FPGAs), memory units, logic gates, registers, semiconductor devices, chips, microchips, chipsets, etc. Examples of software elements may include software components, programs, applications, computer programs, application programs, system programs, software development programs, machine programs, operating system software, middleware, firmware, software modules, routines, subroutines, functions, methods, processes, software interfaces, application program interfaces (APIs), instruction sets, computed code, computer code, code segments, computer code segments, words, values, symbols, or any combination thereof. However, determining whether an embodiment is implemented using hardware and / or software elements can depend on many factors, such as desired computing speed, power level, heat resistance, processing cycle budget, input data rate, output data rate, memory resources, data bus speed, and other design or performance constraints desired according to a given embodiment.

[0114] One or more aspects of at least one embodiment can be implemented by representative instructions stored in a machine-readable medium, which represent various logics within a processor, and when read by a machine, the instructions cause the machine to manufacture the logic and execute the techniques described herein. This representation, referred to as an "IP core," can be stored in a tangible machine-readable medium and provided to various customers or manufacturing facilities for loading into manufacturing machines that manufacture logic or processors. Some embodiments can be implemented, for example, using a machine-readable medium or article, which can store instructions or sets of instructions, and when the instructions or sets of instructions are executed by a machine, the machine can perform the methods and / or operations according to the embodiment. Such a machine may include, for example, any suitable processing platform, computing platform, computing device, processing device, computing system, processing system, computer, processor, etc., and can be implemented in any suitable combination of hardware and / or software. Machine-readable media or articles may include, for example, any suitable type of memory unit, memory device, memory article, memory medium, storage device, storage article, storage medium and / or storage unit, such as memory, removable or non-removable media, erasable or non-erasable media, writable or rewritable media, digital or analog media, hard disks, floppy disks, read-only compact disks (CD-ROMs), recordable compact disks (CD-Rs), rewritable compact disks (CD-RWs), optical disks, magnetic media, magneto-optical media, removable memory cards or disks, various types of digital versatile disks (DVDs), magnetic tapes, cassette tapes, etc.Instructions may include any suitable type of code, such as source code, compiled code, interpreted code, executable code, static code, dynamic code, cryptographic code, etc., and may be implemented in any suitable high-level, low-level, object-oriented, visible, compiled, and / or interpreted programming language.

[0115] The components and features of the above-described device can be implemented using any combination of discrete circuits, application-specific integrated circuits (ASICs), logic gates, and / or single-chip architectures. Where appropriate, the device features may also be implemented using microcontrollers, programmable logic arrays, and / or microprocessors, or any combination thereof. Hardware, firmware, and / or software elements may be collectively referred to as "logic" or simply "circuits" in this paper.

[0116] It should be understood that the exemplary devices shown in the block diagram above may represent just one example of a functional description of many potential embodiments. Therefore, the separation, omission, or inclusion of block functions shown in the diagram does not necessarily mean that hardware components, circuits, software, and / or elements for performing these functions are necessarily separated, omitted, or included in the embodiment.

[0117] At least one computer-readable storage medium may contain instructions that, when executed, cause a system to perform the methods described in this paper.

[0118] Some embodiments may be described using the expression “one embodiment” or “embodiment” and its derivatives. These terms mean that certain features, structures, or characteristics described in relation to the embodiment are included in at least one embodiment. The phrase “in one embodiment” appearing in different parts of the specification does not necessarily refer to the same embodiment. Furthermore, unless otherwise specified, the features described above are considered to be usable in any combination. Thus, any features discussed individually can be used in combination with each other unless one notices that they are incompatible with each other.

[0119] In one embodiment, the optical communication system comprises a sensing and interrogation unit and a plurality of sensing units located in the sensing and interrogation unit and communicably coupled to the sensing and interrogation unit via an optical communication path, wherein the sensing and interrogation unit is configured to transmit an optical signal to the plurality of sensing units, receive a plurality of reflected signals in response to the optical signal, convert the plurality of reflected signals in at least one of the frequency domain and time domain, and use the converted plurality of reflected signals to determine the state of one or more parts.

[0120] In this system, the optical signal is a single-wavelength optical signal.

[0121] In this system, multiple reflected signals are transformed in the frequency domain in order to determine one or more positions corresponding to the approximate positions of reflected signals included in multiple reflected signals in an optical communication path.

[0122] In this system, multiple reflected signals converted in the frequency domain are converted in the time domain to determine one or more changes in the reflected signals over a predetermined time period and to determine the precise location of the reflected signals.

[0123] In this system, the conversion of reflected signals between the frequency domain and the time domain is performed by the Fast Fourier Transform.

[0124] In this system, the plurality of reflected signals include at least a portion of a first plurality of reflected signals received in a first time period and at least a portion of a second plurality of reflected signals received in a second time period, the second time period being a time period following the first time period.

[0125] In this system, the sensing and interrogation unit includes a transmission optical device configured to transmit optical signals to a plurality of sensing units.

[0126] In this system, the transmission device includes a laser light source configured to generate an optical signal.

[0127] In this system, the laser light source includes at least one of a scanning laser, a continuous wave laser, a multi-tone frequency laser, and any combination thereof.

[0128] In the system, the sensing and interrogation unit includes a receiving optical device configured to be communicatively coupled to an optical transmission path and to receive multiple reflected signals.

[0129] In this system, the optical communication path is a distributed acoustic sensing optical transmission path.

[0130] In this system, the optical signal includes an interrogation signal.

[0131] In one embodiment, a method for monitoring an optical transmission path in an optical transmission system, the optical transmission system comprising a sensing and interrogation unit and a plurality of sensing units located on the optical transmission path, the method may include transmitting an optical signal to the plurality of sensing units, receiving a plurality of reflected signals in response to the optical signal, converting the plurality of reflected signals in at least one of the frequency domain and time domain, and determining the state of one or more parts using the converted plurality of reflected signals.

[0132] In this method, the optical signal is a single-wavelength optical signal.

[0133] In this system, multiple reflected signals are transformed in the frequency domain in order to determine one or more positions corresponding to the approximate positions of reflected signals included in multiple reflected signals in an optical communication path.

[0134] In this system, multiple reflected signals converted in the frequency domain are converted in the time domain to determine one or more changes in the reflected signals over a predetermined time period and to determine the precise location of the reflected signals.

[0135] In this system, the conversion of reflected signals between the frequency domain and the time domain is performed by the Fast Fourier Transform.

[0136] In this system, the multiple reflected signals include at least a portion of the first multiple reflected signals received in the first time period and at least a portion of the second multiple reflected signals received in the second time period, the second time period being a time period following the first time period.

[0137] In the system, the sensing and interrogation unit includes a transmitting optical device configured to transmit optical signals to a plurality of sensing units, and a receiving optical device configured to be communicatively coupled to an optical transmission path and to receive a plurality of reflected signals.

[0138] In the system, the transmission device includes a laser light source configured to generate an optical signal, the laser light source includes at least one of a scanning laser, a continuous wave laser, a multi-tone frequency laser, and any combination thereof.

[0139] It is important to emphasize that this summary of the disclosure is provided to allow the reader to quickly determine the nature of the technical disclosure. As a prerequisite for filing this document, it is understood that this document is not to be used for interpretation or limitation of the claims or their meaning. Furthermore, in the detailed description above, it is evident that various features have been combined into a single embodiment in order to simplify the disclosure. This method of disclosure should not be interpreted as reflecting an intention that the embodiment for which protection is sought requires more features than those explicitly cited in each claim. On the contrary, as reflected in the following claims, the subject matter of inventive step lies in the fact that the features of a single disclosed embodiment are fewer than all of them combined. Therefore, the following claims are incorporated into the detailed specification, and each claim exists independently as a separate embodiment. In the attached claims, the terms “includes” and “contains” are used as pure English equivalents corresponding to the terms “includes” and “contains.” Also, terms such as “first,” “second,” and “third” are used merely as labels and are not intended to impose a numerical requirement on their subject matter.

[0140] The above content includes examples of the disclosed architecture. Of course, it is impossible to describe every conceivable combination of components and / or methods, but those skilled in the art will recognize that many other combinations and arrangements are possible. Therefore, the novel architecture aims to cover all changes, modifications, and variations that fall within the spirit and scope of the attached claims.

[0141] For illustrative and descriptive purposes, the foregoing description of exemplary embodiments is provided. It is not intended to exhaustively enumerate or limit this disclosure to the exact form disclosed. Many modifications and changes are possible with respect to this disclosure. It is intended that the scope of this disclosure is not limited by this detailed description but rather by the appended claims. Future applications claiming priority to this application may request subject matter disclosed in different forms and may typically include any set of one or more limitations disclosed or otherwise demonstrated herein. (Other possible items) (Item 1) Interrogation and sensing unit, The system comprises a plurality of sensing units located in the aforementioned interrogation and sensing unit and communicably coupled to the aforementioned interrogation and sensing unit using an optical communication path, The aforementioned interrogation and sensing unit is In order to determine the state of one or more parts of the optical communication path, optical signals are transmitted to the plurality of sensing units. Multiple reflected signals are received in response to the aforementioned optical signal. The plurality of reflected signals are converted in at least one of the frequency domain and the time domain, The system is configured to determine the state of one or more parts using a plurality of converted reflected signals. Optical communication system. (Item 2) The aforementioned optical signal is a single-wavelength optical signal. The system described in item 1. (Item 3) In order to determine one or more positions corresponding to the approximate positions of the reflected signals included in the plurality of reflected signals in the optical communication path, the plurality of reflected signals are converted in the frequency domain. The system described in item 1. (Item 4) The plurality of reflected signals converted in the frequency domain are, Determine one or more changes in the reflected signal during a predetermined time period, and To determine the precise location of the reflected signal, The transformation in the aforementioned time domain The system described in item 3. (Item 5) The transformation of the reflected signal in the frequency domain and the time domain is performed by the Fast Fourier Transform. The system described in item 4. (Item 6) The plurality of reflected signals include at least a portion of the first plurality of reflected signals received in the first time period and at least a portion of the second plurality of reflected signals received in the second time period, wherein the second time period is a time period after the first time period. The system described in item 3. (Item 7) The interrogation and sensing unit includes a transmission optical device configured to transmit the optical signal to the plurality of sensing units. A system described in any one of items 1 through 6. (Item 8) The transmission device includes a laser light source configured to generate the optical signal, A system described in any one of items 1 through 7. (Item 9) The laser light source includes at least one of a scanning laser, a continuous wave laser, a multi-tone frequency laser, and any combination thereof. The system described in item 8. (Item 10) The interrogation and sensing unit includes a receiving optical device configured to be communicatively coupled to the optical transmission path and to receive the plurality of reflected signals. A system described in any one of items 1 through 9. (Item 11) The optical communication path is a distributed acoustic sensing optical transmission path. A system described in any one of items 1 through 10. (Item 12) The optical signal includes an interrogation signal. A system described in any one of items 1 through 11. (Item 13) A method for monitoring an optical transmission path in an optical transmission system comprising an interrogation and sensing unit and a plurality of sensing units located on the optical transmission path, To determine the state of one or more parts of the optical communication path, optical signals are transmitted to the plurality of sensing units. Receiving multiple reflected signals in response to the aforementioned optical signal, Converting the plurality of reflected signals in at least one of the frequency domain and the time domain, This includes determining the state of one or more parts using the converted multiple reflected signals, A method for monitoring optical transmission paths in an optical transmission system. (Item 14) The aforementioned optical signal is a single-wavelength optical signal. The method described in item 13. (Item 15) In order to determine one or more positions corresponding to the approximate positions of the reflected signals included in the plurality of reflected signals in the optical communication path, the plurality of reflected signals are converted in the frequency domain. The method described in item 13. (Item 16) The plurality of reflected signals converted in the frequency domain are, Determine one or more changes in the reflected signal during a predetermined time period, and To determine the precise location of the reflected signal, The transformation in the aforementioned time domain The method described in item 15. (Item 17) The transformation of the reflected signal in the frequency domain and the time domain is performed by the Fast Fourier Transform. The method described in item 16. (Item 18) The plurality of reflected signals include at least a portion of a first plurality of reflected signals received in a first time period and at least a portion of a second plurality of reflected signals received in a second time period, wherein the second time period is a time period following the first time period. The method described in item 15. (Item 19) The aforementioned interrogation and sensing unit is A transmission optical device configured to transmit the optical signal to the plurality of sensing units, Includes a receiving optical device configured to be communicatively coupled to the optical transmission path and to receive the plurality of reflected signals, The method described in any one of items 13 to 18. (Item 20) The transmission optical device includes a laser light source configured to generate the optical signal, the laser light source includes at least one of a scanning laser, a continuous wave laser, a multitone frequency laser, and any combination thereof. The method described in item 19.

Claims

1. Interrogation and sensing unit, The system comprises a plurality of sensing units located in the aforementioned interrogation and sensing unit and communicably coupled to the aforementioned interrogation and sensing unit using an optical communication path, The aforementioned interrogation and sensing unit is In order to determine the state of one or more parts of the optical communication path, optical signals are transmitted to the plurality of sensing units. Multiple reflected signals are received in response to the aforementioned optical signal. The plurality of reflected signals are converted in at least one of the frequency domain and the time domain, The system is configured to determine the state of one or more parts using a plurality of converted reflected signals. Optical communication system.

2. The aforementioned optical signal is a single-wavelength optical signal. The optical communication system according to claim 1.

3. In order to determine one or more positions corresponding to the approximate positions of the reflected signals included in the plurality of reflected signals in the optical communication path, the plurality of reflected signals are converted in the frequency domain. The optical communication system according to claim 1.

4. The plurality of reflected signals converted in the frequency domain are, Determine one or more changes in the reflected signal during a predetermined time period, and To determine the precise location of the reflected signal, The transformation in the aforementioned time domain The optical communication system according to claim 3.

5. The transformation of the reflected signal in the frequency domain and the time domain is performed by the Fast Fourier Transform. The optical communication system according to claim 4.

6. The plurality of reflected signals include at least a portion of the first plurality of reflected signals received in a first time period and at least a portion of the second plurality of reflected signals received in a second time period, wherein the second time period is a time period following the first time period. The optical communication system according to claim 3.

7. The interrogation and sensing unit includes a transmission optical device configured to transmit the optical signal to the plurality of sensing units. The optical communication system according to claim 1.

8. The optical transmission device includes a laser light source configured to generate the optical signal, The optical communication system according to claim 7.

9. The laser light source includes at least one of a scanning laser, a continuous wave laser, a multi-tone frequency laser, and any combination thereof. The optical communication system according to claim 8.

10. The interrogation and sensing unit includes a receiving optical device configured to be communicatively coupled to the optical transmission path and to receive the plurality of reflected signals. The optical communication system according to claim 1.

11. The optical communication path is a distributed acoustic sensing optical transmission path. The optical communication system according to claim 1.

12. The optical signal includes an interrogation signal. The optical communication system according to any one of claims 1 to 11.

13. A method for monitoring an optical transmission path in an optical transmission system comprising an interrogation and sensing unit and a plurality of sensing units located on the optical transmission path, To determine the state of one or more parts of the optical communication path, optical signals are transmitted to the plurality of sensing units. Receiving multiple reflected signals in response to the aforementioned optical signal, Converting the plurality of reflected signals in at least one of the frequency domain and the time domain, This includes determining the state of one or more parts using the converted multiple reflected signals, A method for monitoring optical transmission paths in an optical transmission system.

14. The aforementioned optical signal is a single-wavelength optical signal. The method according to claim 13.

15. In order to determine one or more positions corresponding to the approximate positions of the reflected signals included in the plurality of reflected signals in the optical communication path, the plurality of reflected signals are converted in the frequency domain. The method according to claim 13.

16. The plurality of reflected signals converted in the frequency domain are, Determine one or more changes in the reflected signal during a predetermined time period, and To determine the precise location of the reflected signal, The transformation in the aforementioned time domain The method according to claim 15.

17. The transformation of the reflected signal in the frequency domain and the time domain is performed by the Fast Fourier Transform. The method according to claim 16.

18. The plurality of reflected signals include at least a portion of the first plurality of reflected signals received in a first time period and at least a portion of the second plurality of reflected signals received in a second time period, wherein the second time period is a time period following the first time period. The method according to claim 15.

19. The aforementioned interrogation and sensing unit is A transmission optical device configured to transmit the optical signal to the plurality of sensing units, Includes a receiving optical device configured to be communicatively coupled to the optical transmission path and to receive the plurality of reflected signals, The method according to any one of claims 13 to 18.

20. The transmission optical device includes a laser light source configured to generate the optical signal, the laser light source includes at least one of a scanning laser, a continuous wave laser, a multitone frequency laser, and any combination thereof. The method according to claim 19.

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