US-12618993-B2 - Relaying apparatus including a fiber sensing system for submarine use

US12618993B2US 12618993 B2US12618993 B2US 12618993B2US-12618993-B2

Abstract

A fiber sensing system according to the present disclosure includes a submarine cable, and a plurality of relaying apparatuses being connected in series to one another via the submarine cable. The relaying apparatus includes a DAS interrogator being connected to a relaying apparatus at a subsequent stage via a sensing optical fiber in the submarine cable, and a terminator being connected to a relaying apparatus at a preceding stage via the sensing optical fiber. The DAS interrogator outputs probe light to the sensing optical fiber. The terminator terminates probe light being output from the DAS interrogator in the relaying apparatus at the preceding stage to the sensing optical fiber. The DAS interrogator receives backscattered light of probe light from the sensing optical fiber, and acquires the DAS data from the received backscattered light.

Inventors

Masafumi EMURA
Yuta Sawai
Hiroki Tanaka
Minoru Kobayashi

Assignees

NEC CORPORATION

Dates

Publication Date: 20260505
Application Date: 20231011
Priority Date: 20221021

Claims (10)

1 . A fiber sensing system comprising: a submarine cable; and a plurality of relaying apparatuses configured to be connected in series to one another via the submarine cable, wherein the submarine cable includes a sensing optical fiber, each of the plurality of relaying apparatuses includes a distributed acoustic sensing (DAS) interrogator configured to be connected to a relaying apparatus at a subsequent stage via the sensing optical fiber, and a terminator being connected to a corresponding relaying apparatus of the plurality of relaying apparatuses at a preceding stage via the sensing optical fiber, the DAS interrogator outputs probe light to the sensing optical fiber being connected to the relaying apparatus at the subsequent stage, the terminator terminates probe light being output from the DAS interrogator in the relaying apparatus at the preceding stage to the sensing optical fiber being connected to the relaying apparatus at the preceding stage in such a way that the probe light is not reflected at an end portion of the sensing optical fiber, and the DAS interrogator receives backscattered light of probe light from the sensing optical fiber being connected to the relaying apparatus at the subsequent stage, and acquires, from the received backscattered light, DAS data representing vibration applied to the sensing optical fiber being connected to the relaying apparatus at the subsequent stage.
2 . The fiber sensing system according to claim 1 , wherein the submarine cable further includes a communication optical fiber, and each of the plurality of relaying apparatuses further includes a network switch that is connected to the communication optical fiber and transmits the DAS data to a predetermined destination via the communication optical fiber.
3 . The fiber sensing system according to claim 2 , wherein each of the plurality of relaying apparatuses further includes a controller that controls the DAS interrogator in such a way as to acquire the DAS data and temporarily stores the DAS data acquired by the DAS interrogator, and the network switch transmits the temporarily stored DAS data to the predetermined destination.
4 . The fiber sensing system according to claim 1 , wherein the sensing optical fiber is an optical fiber with increased sensitivity by adding impurities.
5 . The fiber sensing system according to claim 1 , wherein the DAS data are data representing vibration applied to the sensing optical fiber due to an acoustic signal transmitted as a carrier wave from an underwater communication device mounted on an underwater unmanned vehicle.
6 . A relaying apparatus among a plurality of relaying apparatuses being connected in series to one another via a submarine cable, the relaying apparatus comprising: a distributed acoustic sensing (DAS) interrogator configured to be connected to a relaying apparatus at a subsequent stage via a sensing optical fiber included in the submarine cable; and a terminator configured to be connected to a corresponding relaying apparatus of the plurality of relaying apparatuses at a preceding stage via the sensing optical fiber, wherein the DAS interrogator outputs probe light to the sensing optical fiber being connected to the relaying apparatus at the subsequent stage, the terminator terminates probe light being output from the DAS interrogator in the relaying apparatus at the preceding stage to the sensing optical fiber being connected to the relaying apparatus at the preceding stage in such a way that the probe light is not reflected at an end portion of the sensing optical fiber, and the DAS interrogator receives backscattered light of probe light from the sensing optical fiber being connected to the relaying apparatus at the subsequent stage, and acquires, from the received backscattered light, DAS data representing vibration applied to the sensing optical fiber being connected to the relaying apparatus at the subsequent stage.
7 . The relaying apparatus according to claim 6 , further comprising a network switch configured to be connected to a communication optical fiber included in the submarine cable and transmit the DAS data to a predetermined destination via the communication optical fiber.
8 . The relaying apparatus according to claim 7 , further comprising a controller configured to control the DAS interrogator in such a way as to acquire the DAS data and temporarily store the DAS data acquired by the DAS interrogator, wherein the network switch transmits the temporarily stored DAS data to the predetermined destination.
9 . The relaying apparatus according to claim 6 , wherein the DAS data are data representing vibration applied to the sensing optical fiber due to an acoustic signal transmitted as a carrier wave from an underwater communication device mounted on an underwater unmanned vehicle.
10 . A fiber sensing method being executed by one relaying apparatus of a plurality of relaying apparatuses being connected in series to one another via a submarine cable, wherein the relaying apparatus includes a distributed acoustic sensing (DAS) interrogator configured to be connected to a relaying apparatus at a subsequent stage via a sensing optical fiber included in the submarine cable, and a terminator configured to be connected to a corresponding relaying apparatus of the plurality of relaying apparatuses at a preceding stage via the sensing optical fiber, and the fiber sensing method comprising: by the DAS interrogator, outputting probe light to the sensing optical fiber being connected to the relaying apparatus at the subsequent stage; by the terminator, terminating probe light being output from the DAS interrogator in the relaying apparatus at the preceding stage to the sensing optical fiber being connected to the relaying apparatus at the preceding stage in such a way that the probe light is not reflected at an end portion of the sensing optical fiber; and by the DAS interrogator, receiving backscattered light of probe light from the sensing optical fiber being connected to the relaying apparatus at the subsequent stage, and acquiring, from the received backscattered light, DAS data representing vibration applied to the sensing optical fiber being connected to the relaying apparatus at the subsequent stage.

Description

INCORPORATION BY REFERENCE This application is based upon and claims the benefit of priority from Japanese patent application No. 2022-169207, filed on Oct. 21, 2022, the disclosure of which is incorporated herein in its entirety by reference. TECHNICAL FIELD The present disclosure relates to a fiber sensing system, a relaying apparatus, and a fiber sensing method. BACKGROUND ART In recent years, a fiber sensing system using a distributed acoustic sensing (DAS) interrogator that acquires environment information representing an environment of an optical fiber has been researched and developed. Specifically, the DAS interrogator receives backscattered light in an optical fiber, utilizes the received backscattered light, and thereby acquires, as the environment information, DAS data representing vibration (including sound, hereinafter the same) being applied to the optical fiber. In addition, recently, since sensitivity of an optical fiber has been improved, research on practical application of a fiber sensing system using a DAS interrogator as an environment monitoring system for land use has been advanced. In addition, research on applying a fiber sensing system using a DAS interrogator into the sea also has been advanced (e.g., International Patent Publication No. WO2021/153142). In this case, the DAS interrogator uses backscattered light in an optical fiber included in a submarine cable, and thereby acquires DAS data. Herein, when a fiber sensing system using a DAS interrogator is applied into the sea, and a sound of an underwater organism, noise of marine traffic, and the like are monitored, monitoring can be performed with high accuracy by using a feature element existing in a higher frequency band. However, due to a principle of fiber sensing, when the DAS interrogator lengthens a section of a submarine cable acquiring DAS data, there is a limitation that DAS data representing vibration in a high frequency band cannot be acquired. In addition, there is also a limitation on a location where the DAS interrogator is installed in the sea. Therefore, in a fiber sensing system according to the related art, there is a problem that a limitation exists on a frequency in DAS data that can be acquired in the sea. SUMMARY Thus, in view of the above-described problem, an example object of the present disclosure is to provide a fiber sensing system, a relaying apparatus, and a fiber sensing method that are capable of acquiring DAS data representing vibration in a high frequency band in the sea. In a first example aspect, a fiber sensing system includes: a submarine cable; anda plurality of relaying apparatuses configured to be connected in series to one another via the submarine cable, whereinthe submarine cable includes a sensing optical fiber,each of the plurality of relaying apparatuses includes a distributed acoustic sensing (DAS) interrogator configured to be connected to a relaying apparatus at a subsequent stage via the sensing optical fiber, anda terminator configured to be connected to a relaying apparatus at a preceding stage via the sensing optical fiber, the DAS interrogator outputs probe light to the sensing optical fiber being connected to the relaying apparatus at the subsequent stage,the terminator terminates probe light being output from the DAS interrogator in the relaying apparatus at the preceding stage to the sensing optical fiber being connected to the relaying apparatus at the preceding stage in such a way that the probe light is not reflected at an end portion of the sensing optical fiber, andthe DAS interrogator receives backscattered light of probe light from the sensing optical fiber being connected to the relaying apparatus at the subsequent stage, and acquires, from the received backscattered light, DAS data representing vibration applied to the sensing optical fiber being connected to the relaying apparatus at the subsequent stage. In a second example aspect, a relaying apparatus is one relaying apparatus of a plurality of relaying apparatuses being connected in series to one another via a submarine cable, and includes: a distributed acoustic sensing (DAS) interrogator configured to be connected to a relaying apparatus at a subsequent stage via a sensing optical fiber included in the submarine cable; anda terminator configured to be connected to a relaying apparatus at a preceding stage via the sensing optical fiber, whereinthe DAS interrogator outputs probe light to the sensing optical fiber being connected to the relaying apparatus at the subsequent stage,the terminator terminates probe light being output from the DAS interrogator in the relaying apparatus at the preceding stage to the sensing optical fiber being connected to the relaying apparatus at the preceding stage in such a way that the probe light is not reflected at an end portion of the sensing optical fiber, andthe DAS interrogator receives backscattered light of probe light from the sensing optical fiber bei