Interrogator unit for multi-span distributed acoustic sensing

Abstract

To provide an interrogator unit for multi-span distributed acoustic sensing, an optical communication system, and a method.SOLUTION: The system includes a distributed acoustic sensing (DAS) interrogation unit. The DAS interrogation unit is configured to generate one or more optical signals for determining a status of one or more portions of an optical communication path, modulate one or more optical signals using one or more measurement pulses, generate one or more modulated optical signals, and transmit one or more modulated optical signals to the one or more portions of the optical communication path. The status of one or more portions of the optical communication path is determined based on one or more reflected signals reflected by one or more portions of the optical communication path in response to one or more modulated optical signals.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present disclosure relates generally to fiber optic communication systems, and more particularly to distributed acoustic sensing, and more particularly to an interrogator unit for performing distributed acoustic sensing (DAS) on multiple optical fiber spans in such systems that include multiple optical amplifier pairs along a measurement path, and more particularly to a method for performing multi-span sensing in such systems using an interrogator unit. [Background technology]

[0002] In a distributed acoustic sensing (DAS) system, a cable containing optical fiber can be used to provide real-time or near-real-time distributed strain sensing. In other words, the cable itself can be used as a sensing element to detect or monitor different types of disruptions, interference, irregularities, activity, man-made or naturally occurring events, acoustic vibrations, etc. in a DAS environment (e.g., land environment, undersea environment). Therefore, a photoelectric device coupled to the optical fiber cable of a DAS system can detect and process reflected optical signals (e.g., audio distortion signals) at specific distances in the DAS environment.

[0003] For example, a DAS system may be based on Rayleigh backscattering (also called a Rayleigh scattering-based DAS system). In such a system, a coherent laser pulse can be transmitted along an optical fiber, and scattering sites within the optical fiber allow the optical fiber to function as a dispersive interferometer, e.g., its gauge length is 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 transmitting the laser pulse, which is called a coherent optical time-domain reflectometer (COTDR).

[0004] In some existing systems, telecommunication optical fibers are utilized as distributed sensors to continuously detect long-distance spatial interference along the transmission / sensing optical fiber in real time. However, typical sensing systems generally require multiple distributed acoustic sensing interrogation units operating at different wavelengths to sense different portions of the optical fiber, which increases the substantial structural and operational complexity of the sensing system when sensing interference, especially when there are interference elements (e.g., optical amplifiers) along the cable, resulting in a higher error rate. Summary of the Invention [Means for solving the problem]

[0005] In some embodiments, the current subject matter relates to an optical communication system. The system may include a distributed acoustic sensing (DAS) interrogation unit. The DAS interrogation unit may be configured to generate one or more optical signals for determining a state of one or more portions of an optical communication path, modulate the one or more optical signals with one or more measurement pulses, generate one or more modulated optical signals, and transmit the one or more modulated optical signals to one or more portions of the optical communication path. The state of the one or more portions of the optical communication path may be determined based on one or more reflected signals reflected by the one or more portions of the optical communication path in response to the one or more modulated optical signals.

[0006] In some embodiments, the current subject matter may include one or more of the following preferred features: The optical communication path may be a distributed acoustic sensing optical transmission path. The DAS interrogation unit may include a transmitting optical device configured to transmit one or more modulated optical signals to one or more portions of the optical communication path. The transmitting device may include a laser source configured to generate one or more optical signals for determining a status of the one or more portions of the optical communication path. The laser source may include at least one of a swept laser, a continuous wave laser, a multi-tone frequency laser, and any combination thereof.

[0007] In some embodiments, the transmitting device may include a pulse generator configured to generate one or more measurement pulses for modulating the one or more optical signals. The transmitting device may include a modulator configured to modulate the one or more optical signals using the one or more measurement pulses generated by the pulse generator. The modulator may include at least one of an acousto-optic modulator, an electro-absorption modulator, an electro-optic modulator (EOM), and any combination thereof. A frequency of at least one modulated optical signal of the one or more modulated optical signals may be determined based on at least one portion of the optical communication path, of one or more portions of the optical communication path, and the at least one modulated optical signal may be used to determine a state of the at least one portion.

[0008] In some embodiments, the DAS interrogator unit may include one or more receiving optical devices communicatively coupled to the optical transmission path and configured to receive a plurality of backscattered signals generated by one or more respective portions of the optical transmission path in response to one or more modulated optical signals transmitted by the transmitting optical device.

[0009] In some embodiments, the one or more optical signals may include an interrogation signal.

[0010] In some embodiments, the present subject matter relates to a method for monitoring an optical transmission path in an optical transmission system, where the optical transmission system may include a distributed acoustic sensing (DAS) interrogation unit. The method includes generating one or more optical signals for determining a status of one or more portions of the optical communication path, modulating the one or more optical signals with one or more measurement pulses to generate one or more modulated optical signals, transmitting the one or more modulated optical signals to the one or more portions of the optical communication path, and determining the status of the one or more portions of the optical communication path based on one or more reflected signals reflected by the one or more portions of the optical communication path in response to the one or more modulated optical signals. In some embodiments, the present subject matter may include one or more preferred features discussed above.

[0011] The details of one or more variations of the subject matter described herein are set forth in the drawings and the description below. Other features and advantages of the subject matter described herein will become apparent from the description, drawings, and claims. [Brief explanation of the drawings]

[0012] The drawings, which are incorporated in and constitute a part of this specification, illustrate certain aspects of the presently disclosed subject matter and, together with the description, contribute to understanding certain principles related to the disclosed embodiments.

[0013] [Figure 1] 1 illustrates an exemplary optical communication system. [Figure 2a] An example of a sensing system that performs multi-span sensing by implementing multiple DAS interrogator units is shown, including time synchronization between the multiple interrogator units. [Figure 2b] An example of a sensing system that performs multi-span sensing by implementing multiple DAS interrogator units is shown, including time synchronization between the multiple interrogator units. [Figure 2c] 2a-b show example amplitude-time diagrams illustrating different wavelengths of signals received by the receiver in the sensing system of FIG. 2a-b, including one or more time offsets between the return signals of each wavelength due to the time synchronization shown in FIG. 2a. [Figure 3] 1 illustrates an example of a sensing system that performs multi-span sensing by implementing a single DAS transmission component in a DAS interrogator unit, according to some embodiments of the current subject matter. [Figure 4] 4 illustrates an exemplary structure of the DAS transmitter shown in FIG. 3, according to some embodiments of the current subject matter. [Figure 5a] 5 shows an exemplary diagram illustrating continuously increasing laser sweep frequencies produced using the swept laser shown in FIG. 4, according to some embodiments of the current subject matter. [Figure 5b] 5 shows an exemplary diagram illustrating stepped increasing frequencies generated using the swept laser shown in FIG. 4, according to some embodiments of the current subject matter. [Figure 6a] 5b shows an exemplary diagram of step increases in laser sweep frequency and DAS signal frequency shown in FIG. 5b, according to some embodiments of the current subject matter. [Figure 6b] 6b is a curve diagram showing an enlarged portion of the curve in FIG. 6a. [Figure 7a] 4 illustrates an example of a multi-tone laser source utilized as a multi-wavelength local oscillator for coherent detection on the receiver side of the system shown in FIG. 3, according to some embodiments of the current subject matter. [Figure 7b] 7a illustrates the multi-tone laser source of FIG. 7a utilized as a multi-wavelength laser source on the transmitter side of the system shown in FIG. 3, according to some embodiments of the current subject matter. [Figure 8] 1 illustrates an exemplary method according to some embodiments of the current subject matter. DETAILED DESCRIPTION OF THE INVENTION

[0014] To address these and potential other deficiencies of currently available solutions, one or more embodiments of the current subject matter relate to methods, systems, products, etc., which, among other possible advantages, may also provide an interrogator unit transmitter for a multi-span distributed acoustic sensing (DAS) system, and in particular to an interrogator unit that can include multiple wavelength / multi-frequency components that can be utilized in such a multi-span DAS system.

[0015] In a distributed acoustic sensing (DAS) system, 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). The DAS signal may be referred to as a transmitted DAS signal. The transmitted DAS signal can propagate in a first direction along a first optical fiber of a bidirectional, dedicated, and / or any other optical fiber pair of the optical cable, and can be periodically amplified by one or more optical amplifiers spaced along the optical fiber. Without limitation, an optical fiber pair may refer to an actual optical fiber pair, individual cores and / or modes within the same optical fiber pair, and / or one or more bidirectional transmission signals in the same core, and / or any other type of optical fiber pair.

[0016] In some cases, a DAS system may provide a submarine optical cable to extend the DAS range. For example, the DAS range may be extended by transmitting and / or amplifying a 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, which may be different from the first optical fiber, e.g., via a high-loss loopback (HLLB) architecture and / or an amplified-filtered loopback (AFLB) architecture, and returning and / or amplifying the DAS signal along the same multiple spans to a DAS device. The DAS device may then receive and process the DAS signal to detect and / or determine any changes in the DAS system environment. Additionally, at a predetermined distance along the optical cable (e.g., after the “Nth” amplifier along the optical cable), the transmitted DAS signal may be returned to the DAS device by, e.g., using a HLLB or AFLB architecture to route and / or bypass the DAS signal to a second optical fiber of the optical fiber pair of the optical cable.

[0017] Thus, the greater coverage provided by the extended DAS range allows the DAS system to better monitor undersea related activities. For example, the optical cables of the extended DAS system can be used to detect ("listen") and / or monitor earthquakes, seabed movements, ship signatures, ship passage, anchoring, fishing net dragging, etc. Thus, the optical cables can effectively act 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 a submarine optical communication system.

[0018] In the following description, the terms path and / or link may refer to any type of communication coupling and / or connection, and may include, but are not limited to, optical coupling and / or connection, electrical coupling and / or connection, electro-optical coupling and / or connection, electro-mechanical coupling and / or connection, electro-optical-mechanical coupling and / or connection, and / or any other type of coupling and / or connection capable of transmitting and receiving any type of signal.

[0019] FIG. 1 illustrates an exemplary optical communication system 100, including two optical fibers forming a bidirectional optical fiber pair, distributed optical amplifiers (DAAs) in two directional optical communication paths, and an optical link between the two directional paths in each amplifier pair. The 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 referred to as a long-distance optical communication system. Bidirectional data transmission can be achieved by constructing optical fiber pairs, cores, and / or modes within the optical cable and / or by transmitting one or more channels (e.g., wavelength division multiplexed channels) per optical fiber pair.

[0020] System 100 may include terminals 103 and 105 communicatively coupled using (e.g., unidirectional) optical paths 111, 121. Terminal 103 may include a transmitter 113 and a receiver 123. Similarly, terminal 105 may include a receiver 115 and a transmitter 125. Transmitter 113 of terminal 103 may be communicatively coupled to receiver 115 of terminal 105 via path 111. Transmitter 125 of terminal 105 may be communicatively coupled to receiver 123 of terminal 103 via communication path 121. Paths 111, 121 may form a bidirectional optical fiber pair. For example, optical path 111 may transmit one or more signals, data, information, etc., and / or any combination thereof, in one direction (e.g., from transmitter 113 to receiver 115). Optical path 121 may transmit one or more signals, data, information, etc., and / or any combination thereof in another direction (eg, from transmitter 125 to receiver 123).

[0021] Thus, with respect to terminal 103, optical path 111 may be referred to as the outbound path, and optical path 121 may be referred to as the inbound path. Optical path 111 may include one or more optical fibers 117-1 through 117-n and one or more optical amplifiers 119-1 through 119-n, the latter positioned within corresponding repeaters 131-1 through 131-n. Similarly, optical path 121 may include one or more optical fibers 127-1 through 127-n and one or more optical amplifiers 129-1 through 129-n, the latter positioned within corresponding repeaters 131-1 through 131-n. Optical fibers 117-1 through 117-n and 127-1 through 127-n may be individual segments of a single optical fiber 117 and / or a single optical fiber 127, respectively, where these segments may be formed by coupling amplifiers and optical fibers 117, 127, as shown in FIG. 1 .

[0022] For example, one or more of optical amplifiers 119-1 through 119-n and / or 129-1 through 129-n may be erbium-doped fiber amplifiers (EDFAs) and / or any other optical amplifiers. Also, while transmitters 113, 115 and receivers 123, 125 are shown as separate components, it will be understood that transmitter 113 and / or receiver 123 may be housed together within a single housing and may form a transponder and / or transceiver in terminal 103. Similarly, transmitter 115 and receiver 125 may be housed together within a single housing and may form a transponder and / or transceiver in terminal 105.

[0023] As described above, optical path pairs (e.g., optical paths 111, 121) may be configured as a set of amplifier pairs 119-1 to 119-n and 129-1 to 129-n within repeaters 131-1 to 131-n, which are communicatively coupled to the repeaters using optical fiber pairs 117 (e.g., using optical fibers 117-1 to 117-n) and 127 (e.g., using optical fibers 127-1 to 127-n), which may be included in an optical fiber cable along with other optical fibers and / or optical fiber pairs supporting additional path pairs. As described above and shown in FIG. 1, for example, each repeater 131-1 to 131-n may include at least one corresponding pair of amplifiers 119-1 to 119-n, 129-1 to 129-n for each path pair and / or may include additional amplifiers for additional path pairs. As shown in FIG. 1, for example, repeater 131-1 may include amplifiers 119-1 and 129-1.

[0024] The optical amplifiers 119-1 to 119-n, 129-1 to 129-n may include EDFAs and / or other rare-earth doped optical fiber amplifiers, such as Raman amplifiers or semiconductor optical amplifiers (SOAs). Each repeater 131-1 to 131-n may further include a corresponding coupling path 133-1 to 133-n that can communicatively couple between the optical paths 111 and 121. As used herein, the terms "couple" and / or "coupled" or "communicatively coupled" may broadly refer to 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 imply that the coupled components and / or elements are directly connected to each other.

[0025] It will be understood that the first and second optical fibers correspondingly providing the transmit and return paths may be included within and / or form a bidirectional optical fiber pair. The optical fiber pair may be a separate DAS-dedicated optical fiber pair. Alternatively or additionally, the optical fiber pair may carry a payload, whereby the wavelength of the DAS signal may be outside the payload channel wavelengths so that the DAS signal does not interfere with the payload signal. It will be 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 repeater 131-1 through 131-n.

[0026] Telecommunication optical fibers are used as distributed sensors to realize distributed acoustic sensing (DAS) for real-time continuous detection of spatial interference along long-distance transmission / sensing optical fibers. However, until now, distributed sensing has been limited to optical fiber lengths in the range of approximately 50 km in typical sensing applications, with some research units 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.

[0027] To sense multiple spans in a submarine network, conventional systems typically utilize multiple DAS interrogator units with different wavelengths. The maximum sensing frequency (in a multi-span sensing system) is determined by the sensing distance covered by a particular DAS interrogator unit (not including preamble optical 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 utilizing the same optical filter wavelength. In such systems, preamble optical fiber spans are not counted in the sensing distance because filters at other wavelengths are used to filter Rayleigh backscatter from these spans.

[0028] Additionally, to perform multi-span sensing, some sensing systems utilize time-interleaved optical pulses from different DAS interrogator units. Transmitting pulses from different wavelengths with controlled time offsets not only reduces EDFA transient effects, but also reduces nonlinearities in the transmission / sensing optical fiber. However, the pulse interleaving feature typically requires all DAS interrogator units to utilize a common clock synchronization, which significantly increases extra complexity and cost. Figure 2a shows an example of a sensing system 200 that performs multi-span sensing by implementing multiple DAS interrogator units.

[0029] System 200 may include a DAS transmit component 202, a transmit combiner component 204, a circulator component 206, a receive separator component 210, and a DAS receive component 212. These components may be communicatively coupled to a DAS undersea system 208. DAS undersea system 208 may include one or more optical sensing optical fibers configured to receive one or more sensing signals 209 from a transmit side of system 200 and transmit one or more backscattered or reflected sensing signals 215 to a receive side of system 200.

[0030] 2b, circulator 206 may not be utilized in DAS undersea system 208. Specifically, system 230, which may include a DAS undersea system, may be configured, for example, using one or more optical fiber pairs to be communicatively coupled directly to transmit combiner component 204 via connection 235 and / or to receive separator component 210 via connection 237. Connection 235 may be utilized to carry optical signal 239 to DAS undersea system 208, and connection 237 may be utilized to transmit an optical signal, which may include Rayleigh scattering from the DAS undersea system, that may be coupled to an optical fiber and whose travel direction is opposite to the travel direction of signal 239.

[0031] The DAS transmission component 202 may include one or more DAS transmitters 201(a, b, ..., n). Each transmitter 201 may be configured to generate and transmit a corresponding sensing optical signal 203(a, b, ..., n) at a predetermined wavelength. For example, transmitter 201a may be configured to generate and transmit an optical sensing signal 203a having a wavelength λ1, transmitter 201b may be configured to generate and transmit an optical sensing signal 203b having a wavelength λ2, and transmitter 201n may be configured to generate and transmit an optical sensing signal 203b having a wavelength λ3. nThe wavelengths of the optical sensing signals 203 generated by corresponding transmitters 201 may be the same and / or different. Each transmitter 201 may be configured to generate and transmit an optical sensing signal 203 to determine the condition of a particular segment, portion, and / or span of an optical communication path of a multi-span undersea system 208, where system 208 may include one or more such spans.

[0032] The signal 203 generated and transmitted by the transmitter 201 can be synchronized using one or more clock and / or synchronization components 214, which can be communicatively coupled to the transmitter 201. Each time an optical sensing signal 203 is generated and transmitted by a particular transmitter 201 to determine the status of a particular span of the system 208, the synchronization component 214 records the transmission time of the optical sensing signal 203. The system 200 may also record additional parameters of the signal 203, such as the wavelength, frequency, etc. of the signal 203. The parameters of the signal 203 can be used to determine the span of the system 208 from which the signal was transmitted. This also allows the system 200 to track reflections generated by the span of the system 208 in response to the signal 203.

[0033] During transmission by the DAS transmission components 202, the signals 203 may be conveyed by a transmit combiner component 204. The component 204 may combine multiple optical sensing signals 203 generated by corresponding transmitters 201 into a single optical sensing signal 205 for transmission. The combiner component 204 may be a dense wavelength division multiplexing (DWDM) component and / or any other type of wavelength combining component and / or any combination of components. Within the combined signal 205, in addition to the specific parameters of the signals 201 (e.g., time, wavelength, frequency, etc.), each optical sensing signal 203 may further have an individual signature and / or label indicating the origin of the signal 201 and / or any other information related to its transmission.

[0034] The combined signal 205 can be transmitted to a circulator component 206. The circulator component 206 can route the signal to and from the multi-span undersea system 208. For such routing, the circulator component 206 can include a DAS transmit component 202 side, a DAS receive component 212 side, and a port that can be communicatively coupled to the system 208. For example, the signal 205 from the combiner component 204 can be received at a first port of the circulator component 206 and routed by the circulator component 206 to a second port thereof that is communicatively coupled to the system 208. An optical sensing signal reflected by one or more spans of the system 208 can be received at a second port of the circulator component 206 and routed to a third port of the circulator component 206 for transmission to the DAS receive component 212. It will be understood that the designation of the first, second, and third ports of the circulator component 206 is entirely arbitrary and is provided herein for illustrative purposes only.

[0035] The combined signal 205 can be routed by the circulator component 206 to the system 208 as one or more optical sensing signals 209. One or more signals 209 (particularly, specific portions thereof) can penetrate spans of the system 208. For example, a portion of the one or more signals 209 corresponding to the signal 203a generated / transmitted by the transmitter 201a can be used to sense a first span of the system 208, a portion (e.g., in wavelength and / or time) of the one or more signals 209 corresponding to the signal 203b generated / transmitted by the transmitter 201b can be used to sense a second span of the system 208, and a portion of the one or more signals 209 corresponding to the signal 203n generated / transmitted by the transmitter 201n can be used to sense the nth span of the system 208.

[0036] One or more spans (or all spans) can be configured to cause reflection of a corresponding signal 201, which forms one or more signals 209. For example, a first span in system 208 can reflect a portion of one or more signals 209 corresponding to optical sensing signal 201a, a second span in system 208 can reflect a portion of one or more signals 209 corresponding to optical sensing signal 201b, and an nth span in system 208 can reflect a portion of one or more signals 209 corresponding to optical sensing signal 201n. The one or more reflections generated by a span in system 208 can be due to one or more faults, interference, cable breaks, and / or any other condition. Alternatively or additionally, an optical sensing signal can be reflected by a corresponding span without detecting any condition (e.g., indicating the normal operating status of the span in system 208).

[0037] The reflected signals can be sent to the circulator component 206 as one or more signals 215 and can be received at a second port of the circulator component 206. The circulator component 206 can then route the one or more reflected signals to its third port for transmission as one or more reflected signals 207 to the DAS receiving component 212.

[0038] During reception by the DAS receiving component 212, one or more reflected signals 207 may be transmitted through a receiving separator component 210. The component 210 may separate the one or more reflected signals 207 received from the circulator component 206 into multiple received optical sensing signals 213(a, b, ..., n). The separator component 210 may be a dense wavelength division multiplexing (DWDM) component and / or any other type of wavelength division component, and / or any combination of components. The signal portions included in the reflected signals 207 may be separated into signals 213(a, b, ..., n) by the separator component 210 and sent to specific receiver components 211(a, b, ..., n) of the DAS receiving component 212, which may be selected using such signal parameters.

[0039] Each receiver 211 may be configured to receive a corresponding reflected sensing optical signal 213(a, b, ..., n) based on one or more reflected signal parameters (e.g., time, wavelength, frequency, phase, one or more signatures, labels, and / or any other parameters). For example, receiver 211a may be configured to receive a reflected optical sensing signal 213a having a wavelength λ1, where signal 213a is a reflection of signal 203a reflected by a first span of system 208, receiver 211b may be configured to receive a reflected optical sensing signal 213b having a wavelength λ2, where signal 213b is a reflection of signal 203b reflected by a second span of system 208, and receiver 211n may be configured to receive a reflected optical sensing signal 213b having a wavelength λ2, where signal 213b is a reflection of signal 203b reflected by a second span of system 208. n 2c shows an example amplitude-time diagram 240 of the signal 203n transmitted by the transmitter 201. The receiver 211 may be configured to receive a reflected optical sensing signal 213n having a wavelength λ, where the signal 213n is a reflection of the signal 203n reflected by the Nth span of the system 208. Each receiver 211 may be configured to receive the optical sensing signal 213 and determine the status of the corresponding span of the system 208. The DAS receiving component 212 may be configured to distinguish each received signal using one or more parameters of the received signal 213 (e.g., time, wavelength, frequency, phase, one or more signatures, signs, and / or any other parameters) to determine whether a particular span of the system 208 is in operation and / or has an optical condition (e.g., damage, interference, earthquake condition, etc.). n (n=1, 2, ..., 10). Diagram 240 shows 10 different signal wavelengths, which allow sensing within the 10,000 kilometer (km) length of the optical communication path of system 208 (e.g., each signal wavelength covers 10 spans, each 100 kilometers long).

[0040] As shown in Figure 2c, each DAS wavelength signal may have a short pulse with a small duty cycle, and all 10 wavelengths may be synchronously interleaved in time. In this example, each wavelength covers 1000 km (not including the lead fiber), and the 10 different wavelengths may be within the C and / or L wavelength bands of the EDFA. The channel spacing may be similar to the spacing used for data channels in some existing optical transmission systems (e.g., 50 GHz spacing).

[0041] In some embodiments, the present subject matter can be configured to perform optical sensing in a multi-span undersea optical communication system using a single DAS transmitter. This can significantly reduce the complexity and cost of the optical communication system because only a single signal source and a single modulation section can be utilized. Also, because the DAS interrogator unit does not require dedicated synchronization circuitry for different wavelengths, the optical communication system can perform optical sensing for its communication links / spans in a more efficient manner.

[0042] 3 illustrates an example of a sensing system 300 that performs multi-span sensing by implementing a single DAS transmission component in a DAS interrogator unit, in accordance with some embodiments of the current subject matter. System 300 may be utilized in undersea and / or land-based environments. Specifically, system 300 may be utilized in a DAS environment and utilized to monitor spans and / or portions of one or more optical paths and / or links that may not be directly communicatively coupled to a DAS interrogator unit.

[0043] In some embodiments, during operation, to monitor a sensing span including one or more optical paths and / or portions thereof, a transmitter of the interrogation unit may be configured to generate an interrogation pulse that can be transmitted toward the optical path to be monitored. As discussed herein, the interrogation pulse may be configured to be transmitted by various optical devices (e.g., which may include one or more, and / or any combination of, a circulator, a coupler, a combiner, and / or any other type of optical device). The pulse may be transmitted toward one or more repeaters in the optical path to reach the portion of the optical path that may need to be monitored.

[0044] In response to receiving an interrogation pulse from the interrogation unit transmitter, the sensing span may be configured to reflect and / or backscatter the interrogation pulse along the entire length of the sensing span. The reflected / backscattered signal may be configured to transmit back toward the interrogation unit receiver. Specifically, the reflected / backscattered signal may be transmitted via various optical paths, which may include one or more optical devices (e.g., which may include one or more of a circulator, a coupler, a combiner, and / or any other optical device, and / or any combination thereof). The interrogation unit receiver may be configured to perform an analysis of the received signal to determine whether there is interference, disruption, etc. in the optical path based on the disturbance in the backscattered signal.

[0045] 3 , system 300 may include a DAS transmitting component side 302 having a single DAS transmitter 301, a circulator component 306, a receiving separator component 310, and a DAS receiving component side 312 having multiple DAS receivers 311(a, b, ..., n) based on signal wavelengths. These components may be communicatively coupled to a DAS undersea system 308. DAS undersea system 308 may include one or more optical fibers and may be configured to receive one or more sensing signals 305 from the transmitting side 302 of system 300 and transmit one or more backscattered or reflected sensing signals 315 to the receiving side 312 of system 300.

[0046] The DAS transmitter 301 may be configured to generate and transmit one or more sensing optical signals 305 to determine the status of a particular segment, portion, and / or span of an optical communication path in a multi-span submarine system 308, where the system 308 may include one or more such spans. The system 308 may be similar to the system 100 shown in FIG. 1. The signals 305 may be transmitted in a time-interleaved manner, such as at predetermined time intervals, one after the other, and / or using a predetermined timetable. The signals (and / or each signal transmitted at a particular time interval) may be transmitted using a multi-wavelength source or a tunable laser with a predetermined wavelength and / or wavelengths and / or predetermined frequency(s) (e.g., 200 nm / s (25 GHz / ms) to 400 nm / s (50 GHz / ms) and / or any other frequency). The wavelength(s) / frequency(s) of the optical sensing signals 305 generated by the transmitter 301 may be the same and / or different.

[0047] The system 300 may be configured to record one or more parameters associated with one or more signals 305, which may include, for example, wavelength, frequency, phase, etc. The parameters of the signals 305 may be used to determine the span of the system 308 of the received signal transmission. This also allows the system 300 to track backscatter and / or reflections generated by the span of the system 308 in response to the one or more signals 305, where the backscatter / reflections may be received by one or more receivers 311(a, b, ..., n) at the receiver side 312.

[0048] During a transmission performed by the DAS transmitter 301, one or more signals 305 may be transmitted through a circulator 306. The circulator 306 may route and transmit the one or more signals 305 to a multi-span undersea system 308. Similar to the circulator 206, the circulator component 306 may include ports that can be communicatively coupled to the DAS transmitter 301 on the DAS transmit side 302, the DAS receive component 312 side, and the system 308. For example, one or more signals 305 from the transmitter 301 may be received at a first port of the circulator 306 and routed by the circulator 306 to a second port thereof that is communicatively coupled to the system 308. Optical sensing signals backscattered and / or reflected by one or more spans of the system 308 may be received at a second port of the circulator 306 and routed to a third port of the circulator component 306 for transmission to the DAS receive component 312 side.

[0049] One or more signals 305 are routed by circulator 306 to system 308 as one or more optical sensing signals 309, as described herein, and are available to traverse spans of system 308. One or more spans (or all spans) may be configured to cause backscattering and / or reflection of one or more signals 309, which may return to circulator 306 as one or more signals 315. For example, a first span of system 308 may reflect a first portion of one or more signals 309, a second span of system 308 may reflect a second portion of one or more signals 309, and an Nth span of system 308 may reflect an nth portion of one or more signals 309. The one or more reflections generated by the spans of system 308 may be due to one or more faults, interference, cable breaks, seismic activity, and / or any other condition. Alternatively or additionally, the optical sensing signal may be reflected by the corresponding span without detecting any condition (eg, indicating the normal operating state of the span of the system 308).

[0050] The reflected signals can be sent to the circulator 306 as one or more signals 315 and can be received at a second port of the circulator component 306. The circulator 306 can then route the one or more reflected signals 315 to its third port for transmission as one or more reflected signals 307 to the DAS receiving component 312. The DAS receiving component 312 may include a receiving separator component 310 (e.g., a DWDM and / or any other type of wavelength division component) that can separate the one or more reflected signals 307 into multiple received optical sensing signals 313(a, b, ..., n) and route them to receivers 311(a, b, ..., n).

[0051] Each receiver 311 may be configured to receive a corresponding reflected sensing optical signal 313(a, b, ..., n) based on one or more reflected signal parameters (e.g., time, wavelength, frequency, one or more signatures, labels, and / or any other parameters). For example, receiver 311a may be configured to receive a reflected optical sensing signal 313a having a wavelength λ1, where signal 313a may be a reflection of signal 303a reflected by a first span of system 308, receiver 311b may be configured to receive a reflected optical sensing signal 313b having a wavelength λ2, where signal 313b may be a reflection of signal 303b reflected by a second span of system 308, and receiver 311n may be configured to receive a reflected optical sensing signal 313b having a wavelength λ2, where signal 313b may be a reflection of signal 303b reflected by a second span of system 308. n where signal 313n may be a reflection of signal 303n reflected by the nth span of system 308. Each receiver 311 may be configured to receive optical sensing signals 313 and determine the status of a corresponding span of system 308. DAS receiver 312 may be configured to distinguish each received signal using one or more parameters of the received signals 313 (e.g., time, wavelength, frequency, phase, one or more signatures, signs, and / or any other parameters) to determine whether a particular span of system 308 is operational and / or whether there is an optical condition (e.g., damage, interference, cable break, earthquake condition, etc.).

[0052] Figure 4 illustrates an exemplary structure of the DAS transmitter 301 shown in Figure 3, according to some embodiments of the current subject matter. As mentioned above, the DAS transmitter 301 can be communicatively coupled to a multi-span undersea system 308 (as shown in Figure 3), which may include one or more spans of optical communication optical fiber available for transmitting optical sensing and / or data signals.

[0053] 4, the DAS transmitter 301 may include a swept laser 402, a modulator 404, a pulse train generator 406, and a modulator driver 408. The swept laser 402 can be communicatively coupled to the modulator 404. The pulse train generator 406 can be communicatively coupled to the modulator 404 via the modulator driver 408.

[0054] The swept laser 402 may be configured to perform a scanning process to determine the status of the optical communication path of the system 308. The scanning process may be initiated by the swept laser 402 generating one or more laser / light beam signals 403. The swept laser 402 may generate such light beam signals 403 using one or more predetermined frequencies and / or amplitudes. The light beam signals 403 may be continuous and / or discontinuous. Each of the light beam signals 403 generated by the swept laser 402 may have different and / or the same frequency / amplitude. In some illustrative, non-limiting examples, the swept laser 402 may be a continuous wave laser and / or any other type of laser. Also, the swept laser 402 may be a single frequency swept laser and / or any other type of frequency-based laser.

[0055] In some exemplary, non-limiting embodiments, the swept laser 402 can be configured to generate an optical signal 403 with a wavelength scanning speed in the range of 10 nm / s (1.25 GHz / ms) to 1000 nm / s (125 GHz / ms). This can be achieved with stepper motors and / or MEMS technology. Thus, assuming a wavelength scanning speed of 80 nm / s (10 GHz / ms), the frequency of the swept laser 402 can be offset by 50 GHz in 5 ms intervals to accommodate sensing over a range from a 1000 km span down to an acoustic frequency of 100 Hz.

[0056] The signal 403 may be received by a modulator 404. The modulator 404 may be configured to modulate the optical beam signal 403 received from the swept laser 402 to generate one or more optical pulses. The output of the modulator 404 (i.e., the optical pulses (FIG. 2c)) may be transmitted as one or more signals 305 to the multi-span undersea system 308. The modulation of the optical beam signal 403 may be performed by the modulator 404 using one or more measurement pulses 405 generated by a pulse train generator 406 (and / or amplified by a modulator driver 408). The measurement pulses 405 may be generated by the pulse train generator 406 using one or more of the same and / or different frequencies.

[0057] In some embodiments, the pulse train generator 406 may be configured such that the modulator 404 modulates the optical beam signal 403 such that each pulse generated by the modulator 404 (utilizing the optical beam signal 403 and a measurement pulse mode) can have a different measurement frequency, which can correspondingly sense a particular span of the optical communication path of the system 308.

[0058] The modulator 404 may be an acousto-optic modulator (AOM), also known as a Bragg unit or acousto-optic deflector (AOD), which uses the acousto-optic effect to diffract and / or offset the frequency of the optical beam signal 403 using one or more acoustic waves (e.g., RF). The modulator 404 may be an electro-absorption modulator (EAM), which may be a semiconductor device that can modulate the intensity of the optical beam signal 403 using a voltage. Alternatively or additionally, the modulator 404 may be an electro-optic modulator (EOM), which may be an optical device that can include a signal control component that modulates the optical beam signal 403 using the electro-optic effect. It will be appreciated that any number and / or combination and / or type of modulators may be used to modulate the optical beam signal 403.

[0059] The modulator 404 can be configured to generate any number of pulses from the optical beam signal 403 using a measurement pulse mode generated by the pulse train generator 406. The pulse frequency can be continuous (e.g., the continuous sweep shown in FIG. 5a) and / or time-interleaved (e.g., the stepped sweep shown in FIG. 5b). Also, in some exemplary non-limiting embodiments, the pulse frequencies can be generated sequentially using one or more predetermined intervals (e.g., 50 GHz) within a predetermined sweep window (e.g., 500 GHz) and a predetermined time period (e.g., 50 ms), such that the optical beam signal 403 generated by the laser 402 can be utilized to determine the condition of an optical communication path having a predetermined length (e.g., 10,000 km), where each signal is designed to cover a predetermined segment of the link, such as 1,000 km. Therefore, the first pulse (e.g., 50 GHz, 5 ms) generated based on one or more laser beam signals 403 can be used to sense whether there is any optical condition (e.g., cable break, interference, earthquake event, etc.) in the first segment (e.g., 0 km to 1000 km) of the optical communication path, the second pulse (e.g., 100 GHz, 10 ms) can be used to sense the second segment (1001 km to 2000 km), ... the tenth or final pulse (e.g., 500 GHz, 50 ms) can be used to sense the tenth or final segment (9001 km to 10000 km).

[0060] Based on the specific span of the optical communication path that a particular pulse is configured to sense, each of the generated pulses may be transmitted and / or repeated / repeated (e.g., utilizing one or more repeaters / EDFAs as shown in FIG. 1). The span may backscatter and / or reflect the pulses, which may be received by the receiver 312 of the DAS interrogator unit (as shown in FIG. 3). The receiver 312 (particularly its DAS receiver 311) may be available to process the backscattered / reflected signals based on the wavelength of such signals (after being transmitted and passing through the separator 310). For example, DAS receiver 311a (as shown in FIG. 3) may be configured to process one or more signals backscattered / reflected by a first segment (e.g., 0 km to 1000 km) of the optical communication path of system 308 in response to a first pulse (e.g., 50 GHz, 5 ms), DAS receiver 311b (as shown in FIG. 3) may be configured to process one or more signals backscattered / reflected by a second segment (e.g., 1001 km to 2000 km) of the optical communication path of system 308 in response to a second pulse (e.g., 100 GHz, 10 ms), etc. It will be appreciated that a single DAS receiver may be utilized to process all backscattered / reflected signals from all spans of the optical communication path of system 308.

[0061] Once the end of the scan window (e.g., 500 GHz, 50 ms) is reached, the scanning process can begin repeating from the first segment, thereby starting with the first pulse. Alternatively or additionally, the scanning process can repeat from the end of the scan window and / or as needed. The scanning process can be performed continuously, at a predetermined time, periodically, and / or at any desired time. In some embodiments, the frequency of the optical beam signal 403 generated by the laser 402 can vary from one scan process to another and / or from one sweep to another. Additionally, the mode of the measurement signal 405 generated by the pulse train generator 406 can similarly vary from one scan process to another and / or between sweeps.

[0062] 5a and 5b are exemplary pulse amplitude-time-laser sweep frequency diagrams of a signal generated based on the optical beam signal 403 and the measurement signal 405 generated by the pulse train generator 406. Specifically, FIG. 5a shows a plot 500 illustrating a laser sweep frequency 502 continuously increasing from 0 to 500 GHz at a rate of 50 GHz. As shown in FIG. 5a, the DAS transmitter 302 can generate 10 pulses (based on the mode of the measurement signal 405 generated by the pulse train generator 406), and the plot 500 displays each pulse amplitude 504 as a vertical band.

[0063] 5b shows a plot 510 illustrating the laser sweep frequency 512, which also increases continuously in steps (e.g., time-interleaved) from 0 to 500 GHz at a rate of 50 GHz. Similarly, the DAS transmitter 302 can generate 10 pulses (based on the mode of the measurement signal 405 generated by the pulse train generator 406), and the plot 510 displays each pulse amplitude 514 as a vertical band. The stepped sweep can be achieved, for example, using a stepper motor and / or MEMS, which can be coupled to the DAS transmitter 302 (e.g., coupled to the pulse train generator 406).

[0064] It is understood that any desired laser sweep frequency may be utilized. For example, the DAS transmitter 302 can achieve a swept laser frequency as high as 16000 nm / s (2 THz / ms) using MEMS laser technology. This can also achieve the instantaneous step sweep shown in FIG. 5b.

[0065] 4, in some embodiments, pulse train generator 406 can align the measurement pulse with optical beam signal 403 generated by laser 402, where the power and frequency of laser 402 may be more stable. This can allow for a more stable frequency offset between one or more local oscillators (LOs) at DAS receiver 312 (as shown in FIG. 3) and one or more Rayleigh return signals from one or more spans generated in response to signal 305. When coherent detection is used, it can also allow one or more digital signal processors at DAS receiver 312 to track large frequency offsets.

[0066] In some embodiments, the present subject matter may be configured to implement a frequency chirp as part of generating the signal pulses transmitted by the transmitter 301. For example, the frequency chirp may be introduced as part of one or more pulses of one or more spans transmitted to the system 308. The frequency chirp may be introduced by a modulator 404 (e.g., an electro-optic modulator (EOM), an acousto-optic modulator (AOM), and / or any other modulator).

[0067] 6a-6b are exemplary pulse amplitude-time-laser sweep frequency diagrams of a signal generated based on the optical beam signal 403 and the measurement signal 405 generated by the pulse train generator 406, where a frequency chirp is introduced by the modulator 404. Specifically, FIG. 6a shows a plot 600 illustrating a laser scanning frequency 602 that increases stepwise from 0 to 500 GHz at a rate of 50 GHz. As shown in FIG. 6a, the DAS transmitter 302 can generate 10 pulses (based on the mode of the measurement signal 405 generated by the pulse train generator 406), and the plot 600 displays each pulse amplitude 604 as a vertical band. The plot 600 also shows the corresponding DAS signal frequency 606.

[0068] The curve 610 shown in FIG. 6b is a signal amplitude diagram. Specifically, a frequency chirp 608 can be introduced during a 20-30 ms time period and in a frequency interval between 249.5 GHz and 250.5 GHz. The frequency signal chirp 608 (±50 MHz) can be introduced within the pulse. The laser frequency 602 can be kept constant throughout the pulse period. In some exemplary embodiments, the frequency chirp can range from a few MHz to 100 MHz, which can be much smaller than the frequency shift that can be generated by laser scanning. The frequency of the frequency chirp 608 can be adjusted to achieve different measurement spatial resolutions. In one or more DAS receivers 311, the chirp pulse train can be associated with a local pulse train that can have the same chirp function. This can allow for improved sensitivity in detecting optical events (e.g., cable breaks, interference, seismic events, etc.).

[0069] In some embodiments, to perform coherent detection at the DAS receiver, a local oscillator (LO) may be included in and / or communicatively coupled to one or more receivers 311. The local oscillator may be implemented with one or more single-frequency laser signal sources. Alternatively, or in addition, a single multi-tone laser signal source may be utilized. In the latter case, DWDM and / or similar optical elements may be used to separate the different reflected signals and route them to the appropriate DAS receiver 311.

[0070] 7a illustrates a multi-tone laser source that can be utilized as a multi-wavelength local oscillator on the receiver side 312 of the system 300 shown in FIG. 3, according to some embodiments of the current subject matter. The system 700 may include a laser source 702 that can be configured to generate a multi-tone signal 701 that can be transmitted to a separator 310. The separator 310 may be a DWDM and / or any other type of separator that can separate the multi-tone signal 701 into multiple signals 703 (a, b, ..., n), where each signal 703 has its own wavelength (e.g., λ1, λ2, ..., λn ) The source 702 may be the same and / or different from the laser 402 shown in FIG. 4. The signal 703 may then be transmitted to a DAS receiver 311 (as shown in FIG. 3) to provide coherent detection of the signal 313 reflected and / or scattered from the corresponding span of the optical communication path. This may allow for a more accurate determination of the state of the span of the system 308.

[0071] 7b illustrates that, according to some embodiments of the current subject matter, the same multi-tone laser source can be utilized as a multi-wavelength laser source on the transmitter side 302 of system 300. Similar to system 700, system 710 may include a laser source 702 capable of generating a multi-tone signal 701, which can be transmitted to a separator 310, which can separate the multi-tone signal 701 into multiple signals 703 (a, b, ..., n), each at a different wavelength (e.g., λ1, λ2, ..., λ n ), the signal 703 can then be transmitted to a corresponding modulator 704 (a, b, ..., n) that modulates the signal 703. The modulator 704 can be similar to the modulator 404 shown in FIG. 4. The modulator 704 outputs a corresponding modulated signal 705 (a, b, ..., n), which can then be combined into a multi-wavelength signal using a combiner 706, which can be sent to the circulator 306 shown in FIG. 3. The combiner 706 can be a DWDM and / or any other type of signal combiner. The combined signal output by the combiner 706 can be sent to the system to be measured by the circulator 306 to sense different spans of the optical communication path 308 shown in FIG. 3.

[0072] 8 illustrates an exemplary process 800 for monitoring an optical transmission path in an optical transmission system, in accordance with some embodiments of the current subject matter. Method 800 can be performed by a DAS interrogation unit (e.g., system 300 shown in FIG. 3). Specifically, the monitoring can be performed by, for example, components of transmitter 301, one or more receivers 311, and any other device including various processors.

[0073] At 802, a DAS interrogation unit (e.g., system 300) may be configured to generate an optical signal. The signal may be generated using one or more lasers 402 shown in FIG. 4 and / or multi-tone laser source 702 shown in FIG. 7b. The one or more lasers 402 / 702 may be provided on the transmitter side of the DAS interrogator unit (e.g., system 300). The lasers may be swept lasers, continuous wave lasers, and / or any other type of laser. Also, the one or more lasers 402 / 702 may be single frequency swept lasers and / or any other type of frequency-based lasers.

[0074] At 804, one or more measurement pulses can be used to modulate the generated one or more optical signals. For example, as shown in FIG. 4 (and / or FIG. 7b), one or more optical signals 403 generated by one or more lasers 402 / 702 can be modulated using a modulator 404. The modulation of the modulator 404 can be achieved based on one or more measurement pulses 405 generated by a pulse train generator 406. As a result of the signal modulation, one or more modulated optical signals can be generated at 806 and transmitted to one or more spans or portions of the optical communication path.

[0075] At 808, one or more modulated optical signals can be transmitted to one or more spans or portions of the optical communication path. At 810, the one or more modulated optical signals can be utilized to determine the status of specific portions of the optical communication path. The status of one or more portions of the optical communication path can be determined at a receiving side of the DAS interrogation unit using one or more reflected and / or backscattered signals reflected by one or more portions of the optical communication path that receive the one or more modulated signals and generate such reflected / backscattered signals in response. The receiving side of the DAS interrogation unit can analyze the reflected / backscattered signals to determine the status of one or more portions of the optical communication path. The analysis can be performed using one or more processing systems at the receiving side of the DAS interrogation unit. Examples of such processing systems may include one or more processors, memory and / or any other storage devices, one or more communication components, one or more input / output components, and may be any combination of hardware and / or software.

[0076] The various elements of the components described above with reference to Figures 1-8 may include various hardware elements, software elements, or a combination of both. 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, computational 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 may vary depending on many factors, such as desired computational speed, power levels, thermal tolerances, processing cycle budgets, input data rates, output data rates, memory resources, data bus speeds, and other design or performance constraints desired according to a given embodiment.

[0077] One or more aspects of at least one embodiment can be implemented by representative instructions stored on a machine-readable medium, which represent various logic within a processor and, when read by a machine, cause the machine to manufacture logic to perform the techniques described herein. This representation, referred to as an "IP core," can be stored on a tangible machine-readable medium and provided to various customers or manufacturing facilities for loading into manufacturing machines that produce the logic or processor. Some embodiments can be implemented, for example, using a machine-readable medium or article that can store instructions or sets of instructions that, when executed by the machine, cause the machine to perform methods and / or operations according to the embodiments. 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 with any suitable combination of hardware and / or software. A machine-readable medium or article 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, for example, memory, removable or non-removable media, erasable or non-erasable media, writable or rewritable media, digital or analog media, hard disk, floppy disk, Compact Disk Read Only Memory (CD-ROM), Compact Disk Recordable (CD-R), Compact Disk Rewriteable (CD-RW), compact disk, magnetic media, magneto-optical media, removable memory cards or disks, various types of Digital Versatile Disks (DVDs), magnetic tape, cassette tape, etc.The instructions may include any suitable type of code, such as source code, compiled code, interpreted code, executable code, static code, dynamic code, encrypted code, etc., and may be implemented in any suitable high-level, low-level, object-oriented, visual, compiled and / or interpreted programming language.

[0078] The components and features of the devices may be implemented using any combination of discrete circuits, application specific integrated circuits (ASICs), logic gates, and / or single-chip architectures. Also, where appropriate, device features may be implemented using microcontrollers, programmable logic arrays, and / or microprocessors, or any combination of the above. It should be noted that hardware, firmware, and / or software elements may be referred to herein collectively or simply as "logic" or "circuitry."

[0079] It should be understood that the exemplary devices shown in the above block diagrams may represent one example of a functional description of many potential embodiments. Thus, the division, omission, or inclusion of block functions depicted in the figures does not imply that hardware components, circuits, software, and / or elements for implementing those functions are necessarily divided, omitted, or included in the embodiment.

[0080] At least one computer-readable storage medium may contain instructions that, when executed, cause the system to perform any of the computer-implemented methods described herein.

[0081] Some embodiments may be described using the phrase "one embodiment" or "embodiment" and its derivatives. These terms mean that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment. The appearance of the phrase "in one embodiment" in different places in the specification does not necessarily refer to the same embodiment. Also, unless otherwise specified, it is contemplated that the features can be used together in any combination. Thus, any features discussed individually can be used in combination with each other, unless noted as being incompatible with each other.

[0082] It should be emphasized that the Abstract of the Disclosure is provided to allow the reader to quickly ascertain the nature of the technical disclosure. Presented herein, this document is not intended to interpret or limit the scope or meaning of the claims. It is also recognized that in the above Detailed Description, various features have been combined into a single embodiment to streamline the disclosure. This method of disclosure should not be interpreted as reflecting an intention that the embodiments for which protection is sought require more features than are expressly recited in each claim. Conversely, as reflected in the following claims, inventive subject matter lies in fewer than all features of a single disclosed embodiment. Accordingly, the following claims are incorporated into the Detailed Description, with each claim standing on its own as a separate embodiment. In the appended claims, the terms "comprising" and "in which" are used as the pure English equivalents of the corresponding terms "comprising" and "in which." Furthermore, the terms "first," "second," "third," etc. are merely used as labels and are not intended to impose numerical requirements on their subject matter.

[0083] The above includes examples of the disclosed architecture. Of course, it is not possible to describe every imaginable combination of components and / or methodologies, but one of ordinary skill in the art will recognize that many other combinations and permutations are possible. Accordingly, the new architecture is intended to cover all such changes, modifications, and variations that fall within the spirit and scope of the appended claims.

[0084] The foregoing description of exemplary embodiments has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure to the precise form disclosed. Many modifications and variations are possible in accordance with this disclosure. It is intended that the scope of the disclosure be limited not by this detailed description, but rather by the appended claims. Future-filed applications claiming priority to this application may claim subject matter disclosed in a different manner and typically may include any set of one or more limitations disclosed or otherwise set forth herein.

Claims

1. 1. An optical communication system comprising a distributed acoustic sensing (DAS) interrogation unit, comprising: The DAS interrogation unit comprises: generating one or more optical signals for determining a state of one or more portions of an optical communication path; modulating the one or more optical signals with one or more measurement pulses to generate one or more modulated optical signals; configured to transmit the one or more modulated optical signals to the one or more portions of the optical communication path; the state of the one or more portions of the optical communication path is determined based on one or more reflected signals reflected by the one or more portions of the optical communication path in response to the one or more modulated optical signals. Optical communication system.

2. The optical communication path is a distributed acoustic sensing optical communication path.

2. The optical communication system according to claim 1.

3. The DAS interrogation unit comprises: a transmitting optical device configured to transmit the one or more modulated optical signals to the one or more portions of the optical communication path; 3. The optical communication system according to claim 2.

4. the transmitting optical device includes a laser source configured to generate the one or more optical signals for determining the condition of the one or more portions of the optical communication path.

4. The optical communication system according to claim 3.

5. The laser source includes at least one of a swept laser, a continuous wave laser, a multi-frequency laser, and any combination thereof; 5. The optical communication system according to claim 4.

6. the transmitting optical device includes a pulse generator configured to generate the one or more measurement pulses for modulating the one or more optical signals; 4. The optical communication system according to claim 3.

7. the transmitting optical device includes a modulator configured to modulate the one or more optical signals with the one or more measurement pulses generated by the pulse generator.

7. The optical communication system according to claim 6.

8. the modulator comprises at least one of an acousto-optic modulator, an electro-absorption modulator, an electro-optic modulator (EOM), and any combination thereof; 8. The optical communication system according to claim 7.

9. The frequency of at least one modulated optical signal of the one or more modulated optical signals is: the one or more portions of the optical communication path are determined based on at least one portion of the optical communication path, and the at least one modulated optical signal is used to determine the state of the at least one portion; 7. The optical communication system according to claim 6.

10. The DAS interrogation unit comprises: one or more receiving optical devices communicatively coupled to the optical communication path and configured to receive a plurality of backscattered signals generated by each of the one or more portions of the optical communication path in response to the one or more modulated optical signals transmitted by the transmitting optical device.

4. The optical communication system according to claim 3.

11. the one or more optical signals include an interrogation signal; 11. An optical communication system according to any one of claims 1 to 10.

12. 1. A method for monitoring an optical communication path in an optical transmission system including a distributed acoustic sensing (DAS) interrogation unit, comprising: generating one or more optical signals for determining a state of one or more portions of an optical communication path; modulating the one or more optical signals with one or more measurement pulses to generate one or more modulated optical signals; transmitting the one or more modulated optical signals to the one or more portions of the optical communication path; determining a state of the one or more portions of the optical communication path based on one or more reflected signals reflected by the one or more portions of the optical communication path in response to the one or more modulated optical signals. A method for monitoring an optical communication path in an optical transmission system.

13. The optical communication path is a distributed acoustic sensing optical communication path. The method of claim 12.

14. The DAS interrogation unit comprises: a transmitting optical device configured to transmit the one or more modulated optical signals to the one or more portions of the optical communication path; The method of claim 13.

15. the transmitting optical device includes a laser source configured to generate one or more optical signals for determining a condition of the one or more portions of the optical communication path; 15. The method of claim 14.

16. The laser source includes at least one of a swept laser, a continuous wave laser, a multi-frequency laser, and any combination thereof; 16. The method of claim 15.

17. The transmitting optical device is a pulse generator configured to generate the one or more measurement pulses for modulating the one or more optical signals; a modulator configured to modulate the one or more optical signals with the one or more measurement pulses generated by the pulse generator, the modulator including at least one of an acousto-optic modulator, an electro-absorption modulator, an electro-optic modulator (EOM), and any combination thereof; 15. The method of claim 14.

18. The frequency of at least one modulated optical signal of the one or more modulated optical signals is: the one or more portions of the optical communication path are determined based on at least one portion of the optical communication path, and the at least one modulated optical signal is used to determine the state of the at least one portion; 18. The method of claim 17.

19. The DAS interrogation unit comprises: one or more receiving optical devices communicatively coupled to the optical communication path and configured to receive a plurality of backscattered signals generated by each of the one or more portions of the optical communication path in response to the one or more modulated optical signals transmitted by the transmitting optical device.

15. The method of claim 14.

20. the one or more optical signals include an interrogation signal; 20. The method of any one of claims 12 to 19.

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