Optical fiber sensing method

Abstract

The objective of the present invention is to provide an optical fiber sensing device and method that enable planar simultaneous measurement of an entire area employing an optical fiber network including a plurality of optical fibers and a plurality of optical switches.　An optical fiber sensing device 301 according to the present invention comprises: one optical pulse tester 10 that outputs optical pulses at an interval T; one sensing optical switch 25 that connects the optical pulse tester 10 to communication optical switches 21 of an existing optical fiber network 100 that includes the plurality of communication optical switches 21, to which a plurality of optical fibers 52 are connected; and a controller 70 that instructs the communication optical switches 21 and the sensing optical switch 25 to switch paths. The controller 70 is characterized by performing distribution control of optical pulses for instructing the switching of the paths such that the optical pulses from the optical pulse tester 10 are sequentially input to all the paths to be sensed, among the paths formed by the optical fibers 52.

Description

Optical fiber sensing method

[0001] The present disclosure relates to fiber optic sensing technology.

[0002] 1 is a diagram illustrating optical fiber sensing. Optical fiber sensing is an optical measurement technique that receives backscattered light 35 generated by test light 30 incident on an optical fiber 50 and measures the distribution of the state of the optical fiber 50. Optical fiber sensing has the following characteristics (see, for example, Non-Patent Document 1):

[0003] Measurements can be made at only one end of the optical fiber (no equipment needs to be installed at the other end). An optical pulse or CW (continuous wave) test light is input and the backscattered light generated in the optical fiber is observed. Backscattered light includes Rayleigh scattering, Brillouin scattering, Raman scattering, etc. When an external disturbance (bending, temperature change, strain, vibration, etc.) is applied to the optical fiber, its state changes, and the state of the backscattered light also changes in response to this state change. Observing the change in the state of the backscattered light is the same as observing the change in the state of the optical fiber, and it is possible to observe the state of the applied disturbance. In other words, by treating the optical fiber as a sensor and observing the backscattered light, it is possible to measure or estimate the disturbance applied to the optical fiber (bending, temperature change, strain change, vibration, etc.). The disturbances that can be measured depend on the measurement method and the type of scattered light being observed.

[0004] For this reason, consideration is being given to treating communication optical fiber networks as sensors and making measurements (see, for example, Non-Patent Document 2). Communication optical fibers are already laid throughout the city, and simply measuring them can be expected to estimate the state of the surrounding environment, and this information can be used in a variety of applications.

[0005] Distributed Acoustic Sensing (DAS) is a known optical fiber sensing technology that uses coherent OTDR. Fig. 2 illustrates a DAS system. The DAS system includes a light source 11, an optical coupler 12, a modulator 13, an optical amplifier 14, an optical circulator 15, an optical fiber 50 to be measured, a control unit 17, a coupler and balance PD 18, a digitizing unit 19, and a computer 20.

[0006] The DAS system of Figure 2 performs coherent detection of backscattered light, thereby obtaining backscattered light waveforms 41, as shown in Figure 3, for the number of incident light pulses. Note that there is a gap D between adjacent backscattered light waveforms 41, which is equal to or greater than the time it takes for light to travel back and forth through the optical fiber 50. In other words, the gap between light pulses incident on the optical fiber is set to be equal to or greater than the time it takes for light to travel back and forth through the optical fiber 50. Adding and averaging these multiple waveforms 41 results in a waveform obtained by a so-called coherent OTDR, enabling high S / N ratio measurements. Meanwhile, arranging these waveforms 41 in pulse order enables the time change in scattered light at each scattering position, i.e., vibration measurement.

[0007] In the DAS system of Fig. 2, optical pulses with different optical frequencies (optical frequency multiplexing) may be input to the optical fiber 50 (FDM DAS). In the case of a single optical frequency, an interval D is required as shown in Fig. 3. However, in the case of optical frequency multiplexing, optical pulses with different optical frequencies can be input to the optical fiber 50 without waiting for the time it takes for the light to travel back and forth through the optical fiber 50 as shown in Fig. 4, so that more waveforms 42 can be input in the same time than in the case of a single optical frequency. １ ~42 ５ In other words, it is possible to shorten the measurement time and improve accuracy by averaging (see, for example, Patent Documents 1 and 2).

[0008] Meanwhile, WDM transmission technology, which multiplexes signals in optical fibers by wavelength, has made it possible to transmit large amounts of data. A device called a ROADM, which uses a wavelength switch that switches the transmission destination depending on the wavelength of the signal, is commonly used, and this controls the transmission and reception direction of the WDM signal. With the aim of opening up networks, an organization called Open ROADM has defined the functions of ROADM (see, for example, Non-Patent Document 3).

[0009] 5 is a diagram illustrating the structure of the ROADM 26. Generally, optical switches such as the ROADM 26 in a WDM transmission system use a wavelength switch 26a on the core network side to select the transmission / reception direction for an optical fiber 52 on the core network side by wavelength. The optical switch includes, for example, an optical branching unit 26b on the user side, and transmits an optical signal from the wavelength switch 26a to an arbitrary user device via the optical branching unit 26b. The optical switch also receives an optical signal from the user device and transmits it to the optical fiber 52 in a direction according to the wavelength.

[0010] Furthermore, APN (all optical network) is also being considered as a future network, in which all signals will be transmitted using WDM and the signal transmission direction will be controlled by an optical switch (see, for example, Non-Patent Document 4).

[0011] JP 2017-026503 A JP 2020-169904 A

[0012] "Advances in distributed vibration sensing for optical communication fiber state visualization," Optical Fiber Technology, Vol. 57, 102263. 2020 "Approach to smart engineering / maintenance aiming for operational innovation," Business Communication, 2022, Vol. 59, No. 4, (https: / / www.bcm.co.jp / site / 2022 / 04 / ntt-as / 2204-ntt-as-01-06.pdf, retrieved June 29, 2023) "Open ROADM Network Model Version 7.1.0", December 16, 2020, (https: / / 0201.nccdn.net / 4_2 / 000 / 000 / 081 / 4ce / open-roadm-network-model-whitepaper-v7.1-v2.1-published-.pdf), retrieved July 5, 2023 "Open All-Photonic Network Functional Architecture”, Version 1.0, 1 / 27 / 2022, (https: / / iowngf.org / wp-content / uploads / formidable / 21 / IOWN-GF-RD-Open-APN-Functional-Architecture-1.0-1.pdf), retrieved July 5, 2023

[0013] The optical fiber sensing technology described above involves injecting test light into a single optical fiber and measuring backscattered light that propagates in the reverse direction through the same optical fiber from various locations within the optical fiber and returns to the optical fiber sensing device. Therefore, when attempting to measure many optical fibers deployed as communication fibers using a single optical fiber sensing device, as in Non-Patent Document 2, optical fiber selection using an optical switch is required, but the following problems arise: (1) Because an optical fiber network includes many optical fibers and optical switches, in order to perform simultaneous, area-wide measurements of an entire area using the optical fiber network using a single optical fiber sensing device, it is necessary to consider the equipment configuration, such as the function, configuration, and wiring of the optical switch. (2) The equipment configuration must not affect the communication function or performance of the optical fiber network. In other words, there is a problem that it is difficult to perform optical fiber sensing on an optical fiber network including multiple optical fibers and multiple optical switches using a single optical fiber sensing device.

[0014] Therefore, in order to solve the above problems, the present invention aims to provide an optical fiber sensing device and method that enables simultaneous, planar measurement of an entire area using an optical fiber network that includes multiple optical fibers and multiple optical switches.

[0015] In order to achieve the above object, the optical fiber sensing device of the present invention selects a communication optical switch included in an optical fiber network using a sensing optical switch, and also controls the communication optical switch so that an optical pulse propagates to a desired optical fiber included in the optical fiber network.

[0016] Specifically, the optical fiber sensing device according to the present invention comprises an optical pulse tester that outputs optical pulses at intervals T; a sensing optical switch that connects the optical pulse tester to a communication optical switch of an existing optical fiber network including a plurality of communication optical switches to which a plurality of optical fibers are connected; and a controller that instructs the communication optical switch and the sensing optical switch to switch paths, wherein the controller controls the distribution of optical pulses that instruct the path switching so that the optical pulses from the optical pulse tester are sequentially input to all paths to be sensed among the paths formed by the optical fibers.

[0017] Furthermore, an optical fiber sensing method according to the present invention comprises the steps of: connecting a plurality of communication optical switches, each connected to a plurality of optical fibers, in an existing optical fiber network via a single sensing optical switch; outputting optical pulses at intervals T from the optical pulse tester; and performing distribution control to instruct the communication optical switch and the sensing optical switch to switch paths so that the optical pulses from the optical pulse tester are sequentially input to all paths to be sensed among the paths formed by the optical fibers.

[0018] This optical fiber sensing device connects the sensing optical switch to any of multiple communication optical switches included in an existing optical fiber network from outside the optical fiber network, so it does not affect the communication functions or performance of the optical fiber network. Furthermore, this optical fiber sensing device performs path switching control not only for the sensing optical switch but also for the communication optical switch, so it can propagate optical pulses to the desired optical fiber.

[0019] Therefore, the present invention can provide an optical fiber sensing device and method that enables simultaneous planar measurement of an entire area using an optical fiber network including multiple optical fibers and multiple optical switches.

[0020] The optical fiber sensing device and method according to the present invention are characterized in that the timing of switching the route in the distribution control is calculated based on the longest length L of the routes, the number M of the communication optical switches, the number N of input ports of the communication optical switch connected to the sensing optical switch, the number n of routes to be sensed connected to the output ports of the communication optical switch, the switching speed ΔT of the communication optical switch, and the switching speed Δt of the sensing optical switch.

[0021] The optical fiber sensing device and method according to the present invention are characterized in that the output port and the input port connected to the path to be sensed are fixedly connected in a 1:1 ratio to the communication optical switch, and the distribution control is performed only by the sensing optical switch. Even if the switching speed of the communication optical switch is slow, sensing is possible in the desired optical fiber for each optical pulse.

[0022] In the optical fiber sensing device and method according to the present invention, the output ports connected to the paths to be sensed in each of the communication optical switches may be divided into a plurality of groups, and the input ports assigned to each group may be assigned to each of the groups, and the optical pulses may be sequentially input to the input ports of each of the groups of the communication optical switch by the sensing optical switch, and the output ports in each of the groups of the communication optical switch may be switched while the input optical pulses make one circuit through the communication optical switch.Even if the switching speed of the communication optical switch is slow, sensing in a desired optical fiber is possible for each optical pulse by utilizing the time it takes the sensing optical switch to make one circuit through the communication optical switch.

[0023] In the optical fiber sensing device and method according to the present invention, the optical pulse may include a plurality of optical frequencies, which can improve the signal-to-noise ratio and measurement accuracy by averaging.

[0024] The optical fiber sensing device and method according to the present invention may further include an optical circulator disposed between the communication optical switch and the sensing optical switch, for inputting backscattered light from the path to be sensed to the optical time domain tester without passing through the sensing optical switch. Since it is not necessary to consider the time required to receive backscattered light, the measurement time can be shortened.

[0025] The above inventions can be combined as much as possible.

[0026] The present invention can provide an optical fiber sensing device and method that enable planar simultaneous measurement of an entire area using an optical fiber network including a plurality of optical fibers and a plurality of optical switches.

[0027] FIG. 1 is a diagram illustrating optical fiber sensing. FIG. 2 is a diagram illustrating a DAS system. FIG. 3 is a diagram illustrating backscattered light acquired with optical pulses of a single optical frequency. FIG. 4 is a diagram illustrating backscattered light acquired with optical pulses of different optical frequencies. FIG. 5 is a diagram illustrating the structure of a ROADM. FIG. 6 is a diagram illustrating a communication optical switch in an optical fiber network. FIG. 7 is a diagram illustrating an example of an optical fiber network. FIG. 8 is a diagram illustrating an optical fiber sensing device according to the present invention. FIG. 9 is a diagram illustrating an optical fiber sensing device according to the present invention. FIG. 10 is a diagram illustrating an optical fiber sensing device according to the present invention. FIG. 11 is a diagram illustrating an optical fiber sensing device according to the present invention. FIG. 12 is a diagram illustrating an optical fiber sensing device according to the present invention. FIG. 13 is a diagram illustrating an optical fiber sensing device according to the present invention. FIG. 14 is a diagram illustrating an optical fiber sensing device according to the present invention. FIG. 15 is a diagram illustrating an optical fiber sensing device according to the present invention. FIG. 16 is a diagram illustrating an optical fiber sensing device according to the present invention.

[0028] The following description of the preferred embodiments of the present invention will be given with reference to the accompanying drawings. The preferred embodiments described below are examples of the present invention, and the present invention is not limited to the preferred embodiments. In this specification and the drawings, components having the same reference numerals are intended to represent the same components.

[0029] [Prerequisites] Communication Optical Switch Figure 6 is a diagram illustrating a communication optical switch 21 in an optical fiber network. The communication optical switch 21 has one side and another side, each equipped with multiple ports. The port on one side is referred to as port 21a, and the port on the other side is referred to as port 21b. The communication optical switch 21 connects port 21a and port 21b in a 1:1 ratio. In this specification, the number of optical fibers connected to port 21a is referred to as N, and the number of optical fibers connected to port 21b is referred to as n.

[0030] Optical Fiber Network FIG. 7 is a diagram illustrating an example of an optical fiber network 100. The optical fiber network 100 is a core network and includes multiple communication optical switches 21, which are connected by optical fibers 52. User devices are connected to the outer side of the outermost communication optical switch 21. The present invention utilizes the optical fibers 52 in such an optical fiber network as sensors. In this case, the sensor may be not only a single optical fiber 52, but also multiple optical fibers 52 connected in series by one or multiple communication optical switches 21. For this reason, in this specification, the optical fiber used as a sensor may be described as a "path." Note that when performing optical fiber sensing, it is not always necessary to use all of the optical fibers 52; it is sufficient to select multiple "paths" to cover an area from which information is desired, and perform optical fiber sensing on those paths.

[0031] ・Sensing optical switch Because the optical fiber (route) to be measured by one optical tester is not necessarily connected to one communication optical switch, a second optical switch (sensing optical switch) is required to select the communication optical switch. The sensing optical switch is connected to all communication optical switches that cover the optical fiber (route) to be measured by the optical tester.

[0032] Optical tester: Because an optical tester is a measuring instrument that inputs test light and measures the light scattered back from it, the same terminal is used to send out test light and receive scattered light. In other words, an optical tester has only one input / output port.

[0033] The present invention is composed of an optical fiber sensing device, an optical tester, a sensing optical switch, and a controller. Here, the sensing optical switch is a switch that is not connected to the communication optical fiber, and therefore can be housed in the same housing as the optical tester. In this specification, an optical fiber sensing device is described as a device in which the optical tester, the sensing optical switch, and the controller are housed in a single housing, but these may not all be housed in a single housing. For example, the sensing optical switch may be located in a dedicated port in the communication optical switch. In this case, the dedicated port to which the optical tester is connected and the part that controls the communication optical switch used for optical fiber sensing are used independently of the optical fiber network communications.

[0034] Whether the sensing optical switch is included in an optical fiber sensing device, a communication optical switch, or exists independently, the optical fibers in an optical fiber network can be measured by controlling the two optical switches with a controller. Measurement is performed while changing the optical fibers in the optical fiber network by switching the two optical switches, so there is no need for an operator to change the optical fiber connection configuration.

[0035] The optical fiber sensing device 301 described below comprises one optical pulse tester 10 that outputs optical pulses at intervals T, one sensing optical switch 25 that connects the optical pulse tester 10 to a plurality of communication optical switches 21 in an existing optical fiber network 100 that includes a plurality of communication optical switches 21 to which a plurality of optical fibers 52 are connected, and a controller 70 that instructs the communication optical switch 21 and the sensing optical switch 25 to switch paths. The controller 70 controls the distribution of optical pulses that instruct the path switching so that the optical pulses from the optical pulse tester 10 are sequentially input to all paths to be sensed among the paths formed by the optical fibers 52.

[0036] The sensing optical switch 25 is connected to a plurality of communication optical fibers 21 (connecting user devices) on the periphery of the optical fiber network 100. The controller 70 controls the interval T between optical pulses output by the optical pulse tester 10, the sensing optical switch 25, and the switching of the communication optical fibers 21.

[0037] Here, the controller 70 is characterized in that it calculates the timing of switching the route in the distribution control based on: the longest length L of the routes; the number M of the communication optical switches 21; the number N of the input ports 21a of the communication optical switch 21 connected to the sensing optical switch 25; the number n of the routes to be sensed connected to the output ports 21b of the communication optical switch 21; the switching speed ΔT of the communication optical switch 21; and the switching speed Δt of the sensing optical switch 25. In any embodiment, the relationship between the interval T of the optical pulses 30 and the switching speed ΔT of the communication optical switch 21 is T>ΔT.

[0038] 8 is a diagram illustrating an optical fiber sensing device 301 according to this embodiment. This embodiment is a configuration in which the communication optical switch 21 has a switching speed that is faster or the same as that of the sensing optical switch 25, or in which a slower switching speed of the communication optical switch 21 is not a problem. This embodiment is also a measurement configuration using a coherent OTDR DAS in which the optical pulse tester 10 outputs optical pulses 30 with a single optical frequency.

[0039] The parameters in this embodiment are as follows: L: length of the longest optical fiber (path), M: number of communication optical switches 21 connected to the sensing optical switch 25, N: number of input ports 21a of the communication optical switch 21 connected to the sensing optical switch 25 (=1), n: number of paths to be sensed connected to the output port 21b of the communication optical switch 21, ΔT: switching speed (switching time) of the communication optical switch 21, Δt: switching speed (switching time) of the sensing optical switch 25, W: pulse width of the optical pulse 30, v: propagation speed of light in the optical fiber.

[0040] Optical pulses 30 are sequentially input to the optical fibers 52 connected to each communication optical switch 21 at intervals T. When changing the communication optical switch 21 into which the optical pulses 30 are to be input, an interval of the switching speed Δt of the sensing optical switch 25 is required. For this reason, the interval T of the optical pulses 30 in one optical fiber 52 １ is (n×T+Δt)×M > T １ >(n×(2L / v+ΔT)+Δt)×M.

[0041] If the path length is on the order of kilometers, the pulse width W of the optical pulse 30 is much smaller than 1 μs and can be ignored. If the sensing optical switch 25 is fast (switching speed Δt is extremely small) and the round-trip time through the path is shorter than the switching speed of the communication optical switch 21 (2L / v<<ΔT), the maximum measurement frequency F is F=1 / (2×(n×(2L / v+ΔT)+Δt))×M)≈1 / (2nΔT×M).

[0042] Conversely, if the time it takes to travel the path back and forth is longer than the switching speed of the communication optical switch 21 (ΔT<<2L / v), the maximum measured frequency F is F=1 / (2×(n×2L / v+Δt)×M)≒1 / (2×(2nL / v)×M).

[0043] [Embodiment 1-2] Figure 9A is a diagram illustrating an optical fiber sensing device 302 according to this embodiment. This embodiment is a configuration in which the communication optical switch 21 has a switching speed that is faster or the same as that of the sensing optical switch 25, or in which a slower switching speed of the communication optical switch 21 is not a problem. This embodiment is also a measurement configuration using a frequency division multiplexing (FDM)-OTDR DAS in which the optical pulse 30 output by the optical pulse tester 10 contains multiple optical frequencies. In the case of FDM OTDR, the waveforms (backscattered light waveforms of each frequency) of embodiment 1-1 can be averaged to improve the SNR and vibration measurement accuracy.

[0044] 9B is a diagram illustrating an optical pulse 30 output by the optical tester 10. Each optical pulse 30 is composed of multiple (m) optical frequency chips (multiplex number m). The width of each optical frequency chip is w, and the width dt of each optical pulse 30 is w × m. Note that parameters not explained here are the same as those explained in embodiment 1-1.

[0045] The interval T between the light pulses 30 in one optical fiber 52 ２ is (n×T+Δt)×M > T ２ >(n×(mw+2L / v+ΔT)+Δt)×M.

[0046] The width w of the optical frequency chip is much smaller than 1 μs if the path length is on the order of km, and the multiplexing number m is negligible since it is in the single digit to 10 range. Furthermore, the maximum measurement frequency F and the like are the same as those explained in embodiment 1-1.

[0047] 10 is a diagram illustrating an optical fiber sensing device 303 according to this embodiment. This embodiment is a configuration for measuring faster vibrations when the communication optical switch 21 has a slower switching speed than the sensing optical switch 25. This embodiment also uses a coherent OTDR DAS for measurement in which the optical pulse tester 10 outputs optical pulses 30 with a single optical frequency.

[0048] The switching speed of the communication optical switch 21 is determined by the communication specifications. Therefore, it may not have the performance required for high-speed waveform acquisition in optical fiber sensing. Therefore, in this embodiment, the communication optical switch 21 is not operated, and the sensing optical switch 25, which is dedicated to sensing, is operated at high speed. Specifically, the controller 70 causes the communication optical switch 21 to establish a fixed 1:1 connection between the output port 21b, to which the path to be sensed is connected, and the input port 21a, and performs distribution control using only the sensing optical switch 25. The optical fiber sensing device 303 can perform optical fiber sensing regardless of the specifications of the optical fiber network 100.

[0049] Parameters not explained here are the same as those explained in embodiment 1-1.

[0050] The number of ports required for the sensing optical switch 25 is M×n. The input port 21a and the output port 21b are connected in advance in a 1:1 ratio within the communication optical switch 21. In other words, a sensing optical fiber (path) is connected to each port of the sensing optical switch 25, and the path (optical fiber 52 and communication optical switch 21) is switched only by the sensing optical switch 25. For this reason, the waveform interval is determined only by the switching speed of the sensing optical switch 25 and the length of the path. In other words, the interval T of the optical pulses 30 in one optical fiber 52 ３ is (n×T+Δt)×M > T ３ >(n×(2L / v+Δt))×M.

[0051] The pulse width W of the optical pulse 30 is negligible because it is much smaller than 1 μs if the path length is on the order of kilometers. The maximum measured frequency F is F=1 / (2×(n2L / v+nΔt)×M)≈1 / (2×(2nL / v)×M), which is the same as in embodiment 1-1.

[0052] [Embodiment 2-2] Figure 11 is a diagram illustrating an optical fiber sensing device 304 of this embodiment. This embodiment is a configuration for when the communication optical switch 21 has a slower switching speed than the sensing optical switch 25 and it is desired to measure faster vibrations. This embodiment also represents a measurement configuration using a frequency division multiplexing (FDM)-OTDR DAS in which the optical pulse 30 output from the optical pulse tester 10 contains multiple optical frequencies. In the case of FDM OTDR, the waveforms (backscattered light waveforms of each frequency) of embodiment 2-1 can be averaged to improve the SNR and vibration measurement accuracy.

[0053] The optical pulse 30 output by the optical tester 10 of this embodiment is as shown in Fig. 9B. The parameters are also the same as those in the previous embodiment.

[0054] The interval T between the light pulses 30 in one optical fiber 52 ４ is (n×T+Δt)×M > T４ >(n×(mw+2L / v+ΔT)+Δt)×M.

[0055] The width w of the optical frequency chip is much smaller than 1 μs if the path length is on the order of km, and the multiplexing number m is negligible since it is in the single digit to 10 range. Furthermore, the maximum measurement frequency F and the like are the same as those explained in embodiment 2-1.

[0056] [Embodiment 3-1] Fig. 12 is a diagram illustrating an optical fiber sensing device 305 of this embodiment. This embodiment also applies when the communication optical switch 21 has a slower switching speed than the sensing optical switch 25 and when it is desired to measure faster vibrations, but it uses fewer input ports 21a than in embodiment 2-1. This embodiment is a measurement configuration using a coherent OTDR DAS in which the optical pulse tester 10 outputs optical pulses 30 with a single optical frequency.

[0057] The controller 70 inputs the optical pulse 30 to one (52-1) of the optical fibers 52 belonging to group 1 among the optical fibers 52 connected to the output port 21b of the first communication optical switch 21-1, and then inputs the optical pulse 30 to one (52-1) of the optical fibers 52 belonging to group 1 among the optical fibers 52 connected to the output port 21b of the second communication optical switch 21-2. This is repeated up to the M-th communication optical switch 21-M.

[0058] Thereafter, the process returns to the first communication optical switch 21-1, and the optical pulse 30 is made incident on the next optical fiber 52-2 belonging to group 1. Subsequently, the optical pulse 30 is made incident on the next optical fiber 52-2 belonging to group 1 of the first communication optical switch 21-2, and this is continued up to the Mth communication optical switch 21-M. After the work for group Gr1 is completed, the same work is performed on group Gr2.

[0059] Here, when Δt>2L / v and Δt×M×N>ΔT, if Δt>max(2L / v, ΔT / MN), port switching in the communication optical switch 21 will be in time. Also, when Δt is much smaller than ΔT, this can be addressed by increasing the number M of communication optical switches 21 or the number N of input ports 21a.

[0060] That is, the controller 70 performs the distribution control by dividing the output ports 21b of each communication optical switch 21, to which the path to be sensed is connected, into a plurality of groups, and setting an input port 21a to be assigned to each group, and by using the sensing optical switch 25 to sequentially input optical pulses 30 to the input ports 21a of each group of the communication optical switch 21, and by switching the output ports 21b in each group of the communication optical switch 21 while the input of the optical pulses 30 makes a circuit of the communication optical switch 21.

[0061] In this embodiment, the interval T between the light pulses 30 in one optical fiber 52 ５ is (2L / v+Δt)×N×M×n / N>T ５ >(2L / v)×M×n. The maximum measurement frequency F is 1 / (2×(2nL / v)×M), which is the same as in the case of embodiment 2-1.

[0062] For example, if L=10 km and ΔT=10 ms, then 2L / v=100 μs<Δt, 10 ms<k×M×100 ns, and N×M is several hundred, then F=5 kHz / nM.

[0063] [Embodiment 3-2] Figure 13 is a diagram illustrating an optical fiber sensing device 306 of this embodiment. This embodiment also applies when the communication optical switch 21 has a slower switching speed than the sensing optical switch 25 and faster vibration measurement is desired, but the number of input ports 21a used is reduced compared to embodiment 2-2. This embodiment also applies to measurements using a frequency division multiplexing (FDM)-OTDR DAS in which the optical pulse tester 10 outputs optical pulses 30 containing multiple optical frequencies. In the case of FDM OTDR, the waveforms (backscattered light waveforms of each frequency) of embodiment 3-1 can be averaged to improve SNR and vibration measurement accuracy.

[0064] The optical pulse 30 output by the optical tester 10 of this embodiment is as shown in Fig. 9B. The parameters are also the same as those in the previous embodiment.

[0065] The interval T between the light pulses 30 in one optical fiber 52 ６ is (n×T+Δt)×M > T ６ >(n×(mw+2L / v+ΔT)+Δt)×M.

[0066] The width w of the optical frequency chip is much smaller than 1 μs if the path length is on the order of km, and the multiplexing number m is negligible since it is in the range of one digit to 10. Furthermore, the maximum measurement frequency F and the like are the same as those explained in embodiment 3-1.

[0067] 14 is a diagram illustrating an optical fiber sensing device 307 of this embodiment. This embodiment is a configuration in which the communication optical switch 21 has a slower switching speed than the sensing optical switch 25 and it is desired to measure faster vibrations, but this configuration uses fewer input ports 21a than in embodiment 2-2 and uses a higher sampling frequency in FDM.

[0068] This embodiment is a measurement configuration using a frequency division multiplexing (FDM)-OTDR DAS in which the optical pulse 30 output from the optical time domain tester 10 contains multiple optical frequencies. The optical pulse 30 output from the optical tester 10 of this embodiment is as shown in Figure 9(B). The parameters are also the same as those in the previously described embodiment.

[0069] The optical time domain tester 10 has an output port 10a that outputs optical pulses 30 and a receiving port 10b that receives backscattered light. The optical fiber sensing device 307 further has an optical circulator 27 that is disposed between the communication optical switch 21 and the sensing optical switch 25 and inputs backscattered light from the path to be sensed to the optical time domain tester 10 without passing through the sensing optical switch 25. In this embodiment, the backscattered light can be acquired at any time using the coupler 28 and the circulator 27, regardless of the operation of the sensing optical switch 25.

[0070] The optical pulse 30 output from the output port 10a of the optical pulse tester 10 is input to each optical fiber 52 (path) by the communication optical switch 21 and the sensing optical switch 25, as described in embodiment 3-2. The major difference between this embodiment and embodiment 3-2 is that in this embodiment, the communication optical switch 21 is changed for each optical frequency chip. For example, an optical frequency chip of the first optical frequency of the optical pulse 30 is input to the optical fiber 52-1 connected to the first communication optical switch 21-1, and then an optical frequency chip of the second optical frequency of the optical pulse 30 is input to the optical fiber 52-1 connected to the second communication optical switch 21-2. In this way, optical chips of different optical frequencies are distributed to each communication optical switch 21-1.

[0071] Meanwhile, the backscattered light from each optical fiber 52 (path) reaches the light-receiving port 10b of the optical pulse tester 10 via a route different from that of the optical pulse 30 due to the circulator 27. This allows the optical pulse tester 10 to input an optical pulse to the next path without waiting for the completion of reception of the backscattered light from a certain path.

[0072] Here, if Δt×m>2L / v and Δt×M×N>ΔT, then Δt>max(2L / vm, ΔT / MN). In other words, if max(2L / v, ΔT / MN)>max(2L / vm, ΔT / MN), and if 2L / vm>ΔT / MN, then the switching speed Δt of the sensing optical switch 25 can be set to 1 / m of that in the third embodiment.

[0073] In this embodiment, the interval T between the light pulses 30 in one optical fiber 52 ７ is Δt×N×M×n / N=ΔtMn>T ７ >2L / vm×Mn.

[0074] The maximum measurement frequency F is m times that of the third embodiment, and therefore F=1 / (2nMΔt)<mv / (4MnL).

[0075] [Embodiment 5] The configuration of the optical fiber sensing device of this embodiment is the same as the optical fiber sensing device 307 described in embodiment 4. The optical fiber sensing device of this embodiment differs from embodiment 4 in the order in which the optical pulses 30 are distributed to each optical fiber 52 (path). Specifically, this embodiment differs from embodiment 4 in that the input port 21a of the communication optical switch 21 is changed for each optical frequency chip.

[0076] For example, an optical frequency chip of the first optical frequency of the optical pulse 30 is input into one optical fiber (52-1) belonging to group Gr1 corresponding to the first input port of the first communication optical switch 21-1, and then an optical frequency chip of the second optical frequency of the optical pulse 30 is input into one optical fiber (52-4) belonging to group Gr2 corresponding to the second input port of the same communication optical switch 21-1. After inputting optical frequency chips into all groups of the communication optical switch 21-1, the same process is performed for the second communication optical switch 21-2. After the process is completed up to the communication optical switch 21-M, the process returns to the communication optical switch 21-1 and optical frequency chips are again distributed from group Gr1. At this time, the optical frequency chip is input into another optical fiber (for example, 52-2) in group Gr1.

[0077] In this embodiment as well, the optical pulse tester 10 can input an optical pulse to the next path without waiting for the completion of reception of backscattered light from a given path.

[0078] The switching speed Δt of the sensing optical switch 25 can be reduced to 1 / m compared to the third embodiment, and the interval between optical pulses 30 in one optical fiber 52 and the maximum measurement frequency F are the same as those described in the fourth embodiment.

[0079] 15 is a diagram illustrating an optical fiber sensing device 308 of this embodiment. The optical fiber sensing device 308 is different from the optical fiber sensing device 307 of FIG. 14 in that the optical coupler 28 is replaced with an optical switch 29. By using the optical switch 29, the optical fiber sensing device 308 can compensate for loss due to the coupler 28. The switching speed of the optical switch 29 is set to be approximately the same as that of the sensing optical switch 25.

[0080] The method of distributing the light pulses, the interval between the light pulses 30 in one optical fiber 52, and the maximum measurement frequency F are the same as those described in the fourth and fifth embodiments.

[0081] Seventh Embodiment Fig. 16 is a diagram illustrating an optical fiber sensing device 309 according to this embodiment. The configuration of the optical fiber sensing device 309 is the same as that of the optical fiber sensing device 305 shown in Fig. 12. The optical fiber sensing device 309 and the optical fiber sensing device 305 have different optical switch switching timings. While the optical fiber sensing device 305 switches the optical fiber 52 (path) for each optical pulse, the optical fiber sensing device 309 switches the optical fiber 52 (path) every predetermined time (e.g., every X seconds). In other words, the optical fiber sensing device 309 continuously inputs an optical pulse 30 into one optical fiber 52 (path) for a predetermined time to perform measurement.

[0082] For example, the optical fiber sensing device 309 performs measurements as follows: For X seconds, multiple optical pulses 30 are continuously injected into one optical fiber (52-1) belonging to group Gr1 corresponding to the first input port of the first communication optical switch 21-1. The optical pulse tester 10 receives backscattered light for each optical pulse 30. After X seconds have passed, multiple optical pulses 30 are continuously injected into one optical fiber (52-1) belonging to group Gr1 corresponding to the first input port of the second communication optical switch 21-2 for X seconds, and measurements are performed in the same manner. After completing measurements up to the Mth communication optical switch 21-M, the device returns to the first communication optical switch 21-1 and continues to inject multiple optical pulses 30 into the next optical fiber (52-2) belonging to group Gr1 corresponding to the first input port for X seconds. This process is repeated up to the Mth communication optical switch 21-M. Then, when group Gr1 is completed, the same process is performed for group Gr2.

[0083] The same optical fiber 52 (route) becomes the measurement target after X×(M×N)=X×n. This means that the more optical fibers 52 (routes), the longer the measurement interval. In this embodiment, since X>ΔT and X>Δt, there are no conditions for the switching speed of the optical switch. Also, the maximum measurement frequency F is v / 4L. The optical pulse 30 may be a single wave or FDM.

[0084] [Example] In the above-described embodiment, the communication optical switch 21 and the sensing optical switch 25 may be optical switches including wavelength control, such as ROADM. The communication optical switch has a WXC (wavelength cross connect) unit on one side, such as a wavelength switch or amplifier, which is difficult to use for optical fiber sensing, and an FXC (fiber cross connect) unit on the other side, whose only function is to switch paths. When optical fiber sensing is performed, it is necessary to realize a connection that avoids the WXC unit. Note that the communication optical switch may also have a configuration that is only an FXC without a WXC.

[0085] As shown in Fig. 17, the optical fiber 52 to be measured in optical fiber sensing may be located on both sides of the communication optical switch 21. Consider a case where such a communication optical switch 21 is a ROADM. The side without a WXC is referred to as the "lower side," and the side with a WXC is referred to as the "upper side." In optical networks, optical switches are sometimes referred to as GWs, and the upper and lower sides are referred to as Ugg (between GW-GW) and Ugt (between GW and Transceiver).

[0086] (Example 1) Figures 18 and 19 are connection configuration examples for explaining this example. The communication optical switch 21 and the sensing optical switch 25 are included in an optical switch called a gateway. The optical time domain tester 10 is connected to the lower part (Ugt side) of a certain gateway. Gateways are connected via Uggs (upper parts). Figure 18 shows an example configuration in which the part corresponding to the sensing optical switch 25 and the part corresponding to the communication optical switch 21 are implemented by the same optical switch. Figure 19 shows an example configuration in which the part corresponding to the sensing optical switch 25 and the part corresponding to the communication optical switch 21 are implemented by physically separate optical switches. In the configuration of Figure 19, the sensing optical switch 25 may be included in the optical time domain tester 10. The optical switch has a turnback 57 that allows loopback. WXC is avoided by a coupler 58.

[0087] (Embodiment 2) Figure 20 shows an example of a connection configuration for explaining this embodiment. The communication optical switch 21 and the sensing optical switch 25 are contained in an optical switch called a gateway. The optical pulse tester 10 is connected to the upper part (Ugg side) of a certain gateway. Gateways are connected via Uggs (upper parts). Figure 20 shows an example of a configuration in which the part corresponding to the sensing optical switch 25 and the part corresponding to the communication optical switch 21 are implemented by the same optical switch. As explained in Figure 19, the part corresponding to the sensing optical switch 25 and the part corresponding to the communication optical switch 21 may be implemented by physically separate optical switches. The optical switch has a turnback 57 that allows for loopback. WXC is avoided by a coupler 58.

[0088] (Embodiment 3) Figure 21 shows an example of a connection configuration for explaining this embodiment. The communication optical switch 21 and the sensing optical switch 25 are included in an optical switch called a GW. The optical pulse tester 10 is connected to the lower part (Ugt side) of a certain GW. The lower part of GW#1 is connected to the upper part of GW#N. Figure 21 shows an example of a configuration in which the part corresponding to the sensing optical switch 25 and the part corresponding to the communication optical switch 21 are implemented by the same optical switch. As explained in Figure 19, the part corresponding to the sensing optical switch 25 and the part corresponding to the communication optical switch 21 may be implemented by physically separate optical switches. Note that the optical switch has a turnback 57 that allows for loopback. WXC is avoided by a coupler 58.

[0089] (Embodiment 4) Figure 22 shows an example of a connection configuration for explaining this embodiment. The communication optical switch 21 and the sensing optical switch 25 are included in an optical switch called a GW. The optical pulse tester 10 is connected to the upper part (Ugg side) of a certain GW. The lower part of GW#1 is connected to the upper part of GW#N. Figure 22 shows an example of a configuration in which the part corresponding to the sensing optical switch 25 and the part corresponding to the communication optical switch 21 are implemented by the same optical switch. As explained in Figure 19, the part corresponding to the sensing optical switch 25 and the part corresponding to the communication optical switch 21 may be implemented by physically separate optical switches. Note that the optical switch has a turnback 57 that allows for loopback. WXC is avoided by a coupler 58.

[0090] (Embodiment 5) Figure 23 shows an example of a connection configuration for explaining this embodiment. The communication optical switch 21 and the sensing optical switch 25 are included in an optical switch called a GW. The optical pulse tester 10 is connected to the lower part (Ugt side) of a certain GW. The lower part of GW#1 is connected to the lower part of GW#N. Figure 23 shows an example of a configuration in which the part corresponding to the sensing optical switch 25 and the part corresponding to the communication optical switch 21 are implemented by the same optical switch. As explained in Figure 19, the part corresponding to the sensing optical switch 25 and the part corresponding to the communication optical switch 21 may be implemented by physically separate optical switches. Note that the optical switch has a turnback 57 that allows for loopback. WXC is avoided by a coupler 58.

[0091] (Example 6) Figure 24 shows an example of a connection configuration for explaining this example. The communication optical switch 21 and the sensing optical switch 25 are included in an optical switch called a gateway. The optical pulse tester 10 is connected to the upper part (Ugg side) of a certain gateway. The lower part of gateway #1 is connected to the lower part of gateway #N. Figure 24 shows an example of a configuration in which the part corresponding to the sensing optical switch 25 and the part corresponding to the communication optical switch 21 are implemented by the same optical switch. As explained in Figure 19, the part corresponding to the sensing optical switch 25 and the part corresponding to the communication optical switch 21 may be implemented by physically separate optical switches. The optical switch has a turnback 57 that allows for loopback. WXC is avoided by a coupler 58.

[0092] Other Embodiments In the above embodiment, a WXC is included in the communication optical switch. In a network in which the communication optical switch does not include a WXC, such as current access networks, by appropriately configuring turnbacks and the like, it is possible to easily connect multiple communication optical switches and perform optical fiber sensing.

[0093] The above examples are configuration examples corresponding to embodiments 1 to 7. By adding an optical circulator 27, an optical coupler 28, and an optical switch 29 to the configurations described in the above examples, the configurations described in embodiments 4 to 6 can also be realized.

[0094] 10: Optical pulse tester 11: Light source 12: Optical coupler 13: Modulator 14: Optical amplifier 15: Optical circulator 17: Control unit 18: Coupler + balanced PD 19: Digitization means 20: Computer 21: Optical switch for communication 25: Optical switch for sensing 27: Optical circulator 28: Optical coupler 29: Optical switch 30: Optical pulse 51, 52: Optical fiber 57: Turn back 58: Optical coupler 70: Controller 100: Optical fiber network 301 to 309: Optical fiber sensing device

Claims

1. An optical fiber sensing device comprising: an optical pulse tester that outputs optical pulses at intervals T; an optical sensing switch that connects the optical pulse tester to a communication optical switch of an existing optical fiber network including multiple communication optical switches to which multiple optical fibers are connected; and a controller that instructs the communication optical switch and the sensing optical switch to switch paths, wherein the controller controls the distribution of optical pulses that instruct the switching of paths so that the optical pulses from the optical pulse tester are sequentially input to all paths to be sensed among the paths composed of the optical fibers.

2. The optical fiber sensing device described in claim 1, characterized in that the controller calculates the timing of switching the route in the distribution control based on: the longest length L of the routes; the number M of the communication optical switches; the number N of input ports of the communication optical switch connected to the sensing optical switch; the number n of routes to be sensed connected to the output ports of the communication optical switch; the switching speed ΔT of the communication optical switch; and the switching speed Δt of the sensing optical switch.

3. The optical fiber sensing device described in claim 2, characterized in that the controller fixedly connects the output port to which the path to be sensed is connected and the input port to the communication optical switch in a 1:1 ratio, and performs the distribution control only using the sensing optical switch.

4. The optical fiber sensing device described in claim 2, characterized in that the controller performs the distribution control by: dividing, in each of the communication optical switches, the output ports to which the path to be sensed is connected into a plurality of groups, and setting the input port responsible for each group; and, in the sensing optical switch, sequentially injecting the optical pulse into the input port for each group of the communication optical switch, and switching the output port in the group of each of the communication optical switches while the injection of the optical pulse makes a circuit around the communication optical switch.

5. An optical fiber sensing device according to any one of claims 1 to 4, characterized in that the optical pulse contains a plurality of optical frequencies.

6. An optical fiber sensing device as described in claim 5, which cites claim 4, further comprising an optical circulator arranged between the communication optical switch and the sensing optical switch, which inputs backscattered light from the path to be sensed to the optical pulse tester without passing through the sensing optical switch.

7. An optical fiber sensing method comprising the steps of: connecting a communication optical switch of an existing optical fiber network including a plurality of communication optical switches to which a plurality of optical fibers are connected and an optical pulse tester through a sensing optical switch; outputting optical pulses at intervals of T from the optical pulse tester; and performing distribution control to instruct the communication optical switch and the sensing optical switch to switch the directions so that the optical pulses from the optical pulse tester are sequentially input to all paths to be sensed among the paths composed of the optical fibers.

8. The optical fiber sensing method described in claim 7, characterized in that the timing of switching the route in the distribution control is calculated based on the longest length L of the routes, the number M of the communication optical switches, the number N of input ports of the communication optical switch connected to the sensing optical switch, the number n of routes to be sensed connected to output ports of the communication optical switch, the switching speed ΔT of the communication optical switch, and the switching speed Δt of the sensing optical switch.

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