Optical fiber vibration sensing device and optical fiber vibration sensing method

Abstract

To provide an optical fiber vibration sensing device and an optical fiber vibration sensing method that achieve optical fiber vibration sensing using an optical fiber interferometer, capable of identifying a location of an optical fiber to which vibration has been added, with a simple configuration.SOLUTION: The optical fiber vibration sensing device measures interference signals with a Mach-Zehnder interferometer on an optical transmission medium having multiple optical transmission paths, each from opposite directions, and identifies the location where the vibration was added by detecting the arrival time difference in accordance with the location where the vibration occurred.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to optical fiber vibration sensing technology using an optical fiber interferometer. [Background technology]

[0002] As a type of optical fiber vibration sensing technology using optical fiber interferometers, a method has been proposed and commercialized in which multiple optical fiber ring interferometers are configured and vibrations are detected on an optical fiber ring interferometer system basis to detect abnormalities such as intrusions (for example, see Non-Patent Document 1).

[0003] As a method for identifying the vibration generation position using an optical fiber interferometer, a method has been proposed in which a sub-loop is added to an optical fiber ring interferometer. By passing through the sub-loop multiple times, multiple optical paths are apparently formed within the same optical fiber ring, and the position can be identified by comparing the interference light output of the light that has passed through each path (for example, see Non-Patent Document 2). [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] Fujikura Engineering Ltd., "Optical Fiber Intrusion Detection System", https: / / www.fen.fujikura.jp / products / pro01 / tel-co-pdf02.pdf (Accessed 2021.1.7) [Non-Patent Document 2] Tatsuya Omori, Hiroaki Ogihara, Kenya Hashimoto, Masatsune Yamaguchi, "Vibration Position Identification Method for Optical Fiber Ring Interferometer Vibration Sensor", IEICE Transactions on Information and Communication Engineers, Vol. J89-B, No. 4, pp. 594-601, 2006 [Non-Patent Document 3] Nobutomo Hanzawa, Kuimasa Saitoh, Taiji Sakamoto, Takashi Matsui, Kyozo Tsujikawa, Masanori Koshiba, and Fumihiko Yamamoto, “Two-mode PLC-based mode multi / demultiplexer for mode and wavelength division multiplexed transmission”, 21 Oct 2013(C) 2013 OSA 4 November 2013 | Vol. 21, No. 22 | DOI:10.1364 / OE.21.025752 | OPTICS EXPRESS 25752 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the device put to practical use in Non-Patent Document 1 requires the installation of a folding device called a branch coupler for each detection section. In order to detect vibrations in a distributed manner, it is necessary to install the required number of branch couplers, which poses a major challenge in terms of installation.

[0006] In addition, in Non-Patent Document 2, it is possible to identify the vibration position. However, since it is premised on applying vibration to one point of the optical fiber ring interferometer, if the entire optical fiber ring interferometer is mounted in a single optical fiber cable that is not in a ring form, vibration will occur in two points, which makes it difficult to apply.

[0007] The present disclosure has been made in light of the above circumstances, and aims to realize optical fiber vibration sensing that has a simple configuration and is capable of identifying the position where vibration is applied. [Means for solving the problem]

[0008] For an optical transmission medium having multiple optical transmission paths, the interference signal is measured using a Mach-Zehnder interferometer from opposite directions, and the location where the vibration was added is identified by detecting the arrival time difference according to the location where the vibration occurred.

[0009] Specifically, the optical fiber vibration sensing device of the present disclosure comprises: an optical transmission medium having a plurality of optical transmission paths; a forward Mach-Zehnder interferometer which, at one end of the optical transmission medium, leaves a portion of the light in fundamental mode as it is and converts the remainder to a higher-order mode, combines the light left in fundamental mode with the converted light in higher-order mode, and inputs the combined light into an optical transmission line, and at the other end of the optical transmission medium, leaves the light in fundamental mode of the light that has propagated through the optical transmission line in fundamental mode and converts the light in higher-order mode to fundamental mode, and combines and receives the light left in fundamental mode with the converted light in fundamental mode; a reverse Mach-Zehnder interferometer which, at the other end of the optical transmission medium, leaves a part of the light in fundamental mode as it is and converts the remainder to a higher-order mode, combines the light left in fundamental mode with the converted light in higher-order mode, and inputs the combined light to another optical transmission path, and at one end of the optical transmission medium, leaves the light in fundamental mode of the light propagating through the other optical transmission path in fundamental mode and converts the light in higher-order mode to fundamental mode, and combines and receives the light left in fundamental mode with the converted light in fundamental mode; Equipped with.

[0010] Specifically, the optical fiber vibration sensing device of the present disclosure comprises: the optical transmission medium includes a first optical transmission path and a second optical transmission path; The forward Mach-Zehnder interferometer comprises: At one end of the optical transmission medium, a forward measurement light source that emits light; a first optical mode coupler that leaves a portion of the fundamental mode light from the forward direction measurement light source as the fundamental mode and converts the remainder into a higher order mode, combines the light that remains in the fundamental mode with the converted light in the higher order mode, and inputs the combined light into the first optical transmission line; At the other end of the optical transmission medium, a second optical mode coupler that, among the light propagating through the first optical transmission line, leaves the light in a fundamental mode as it is and converts the light in a higher order mode to the fundamental mode, and couples the light that remains in the fundamental mode with the converted light in the fundamental mode; a forward direction measurement receiver that receives light from the second optical mode coupler; The reverse Mach-Zehnder interferometer comprises: At the other end of the optical transmission medium, a light source for backward measurement that emits light; a third optical mode coupler that leaves a part of the fundamental mode light from the backward direction measurement light source as the fundamental mode and converts the remainder into a higher order mode, combines the light that remains in the fundamental mode with the converted light in the higher order mode, and inputs the combined light into the second optical transmission line; At one end of the optical transmission medium, a fourth optical mode coupler that, among the light propagating through the second optical transmission line, leaves the light in a fundamental mode as it is and converts the light in a higher order mode to the fundamental mode, and couples the light that remains in the fundamental mode with the converted light in the fundamental mode; a backward direction measurement optical receiver that receives light from the fourth optical mode coupler; The present invention is characterized by comprising:

[0011] Specifically, the optical fiber vibration sensing device of the present disclosure comprises: the optical transmission medium includes a first optical transmission path, a second optical transmission path, a third optical transmission path, and a fourth optical transmission path; The forward Mach-Zehnder interferometer comprises: At one end of the optical transmission medium, a forward measurement light source that emits light; a first optical mode coupler that leaves a part of the fundamental mode light from the forward direction measurement light source as the fundamental mode and converts the remainder into a higher order mode, combines the light that remains in the fundamental mode with the converted light in the higher order mode, and inputs the combined light into the first optical transmission line; a forward direction measurement light receiver that receives light from the third optical transmission line, At the other end of the optical transmission medium, a second optical mode coupler which, among the light propagating through the first optical transmission line, leaves the light in a fundamental mode as it is and converts the light in a higher order mode to the fundamental mode, combines the light that remains in the fundamental mode with the converted light in the fundamental mode, and outputs the combined light to the third optical transmission line; The reverse Mach-Zehnder interferometer comprises: At one end of the optical transmission medium, a light source for backward measurement that transmits light to the fourth optical transmission line; a fourth optical mode coupler that, among the light propagating through the second optical transmission line, leaves the light in a fundamental mode as it is and converts the light in a higher order mode to the fundamental mode, and couples the light that remains in the fundamental mode with the converted light in the fundamental mode; a backward direction measurement optical receiver that receives light from the fourth optical mode coupler, At the other end of the optical transmission medium, a third optical mode coupler that leaves a part of the fundamental mode light from the fourth optical transmission line as the fundamental mode and converts the remainder into a higher-order mode, combines the light that remains in the fundamental mode with the converted light in the higher-order mode, and inputs the combined light into the second optical transmission line; It is characterized by:

[0012] Specifically, the optical fiber vibration sensing device of the present disclosure comprises: The first optical mode coupler or the third optical mode coupler is an off-axis connection part in which the centers of the cores of two optical fibers are connected with each other off-axis. It is characterized by:

[0013] Specifically, the optical fiber vibration sensing device of the present disclosure comprises: An optical fiber on the side of the forward measurement light source of the axially offset connection portion as the first optical mode coupler or on the side of the backward measurement light source of the axially offset connection portion as the third optical mode coupler propagates only light of a fundamental mode. It is characterized by:

[0014] Specifically, the optical fiber vibration sensing device of the present disclosure comprises: As the second optical mode coupler or the fourth optical mode coupler, an off-axis connection section is provided in which the centers of the cores of two optical fibers are connected with an offset, and an optical fiber on the side of the forward direction measurement receiver of the off-axis connection section as the second optical mode coupler or on the side of the reverse direction measurement receiver of the off-axis connection section as the fourth optical mode coupler propagates only light of a fundamental mode. It is characterized by:

[0015] Specifically, the optical fiber vibration sensing device of the present disclosure comprises: the optical transmission medium comprises an optical transmission path, the forward Mach-Zehnder interferometer and the backward Mach-Zehnder interferometer share a fifth optical mode coupler that combines and branches light at one end of the optical transmission medium, and share a sixth optical mode coupler that combines and branches light at the other end of the optical transmission medium; The forward Mach-Zehnder interferometer comprises: At one end of the optical transmission medium, A forward measurement light source is provided to emit light, said fifth optical mode coupler keeps a part of the fundamental mode light from said forward direction measurement light source as the fundamental mode and converts the remainder into a higher order mode, combines the light kept in the fundamental mode with the converted higher order mode light, and inputs the combined light into said optical transmission line; At the other end of the optical transmission medium, a forward direction measurement receiver for receiving light; the sixth optical mode coupler, among the light propagating through the optical transmission line, leaves the light in fundamental mode as it is, converts the light in higher-order modes to fundamental mode, combines the light that remains in the fundamental mode with the converted light in fundamental mode, and outputs the combined light to the forward direction measurement optical receiver; The reverse Mach-Zehnder interferometer comprises: At the other end of the optical transmission medium, a backward measurement light source that emits light of a wavelength different from that of the forward measurement light source; the sixth optical mode coupler keeps a part of the fundamental mode light from the backward measurement light source as the fundamental mode and converts the remainder into a higher-order mode, combines the light kept in the fundamental mode with the converted higher-order mode light, and inputs the combined light into the optical transmission line; At one end of the optical transmission medium, a reverse direction measurement receiver that receives light from the fifth optical mode coupler; Among the light propagating through the optical transmission line in the fifth optical mode coupler, the light in the fundamental mode is left as the fundamental mode, and the light in the higher order mode is converted to the fundamental mode, and the light that is left as the fundamental mode and the converted light in the fundamental mode are combined, and output to the reverse direction measurement optical receiver. It is characterized by:

[0016] Specifically, the optical fiber vibration sensing device of the present disclosure comprises: the optical transmission medium includes a first optical transmission path, a third optical transmission path, and a fourth optical transmission path; the forward Mach-Zehnder interferometer and the backward Mach-Zehnder interferometer share a fifth optical mode coupler that combines and branches light at one end of the optical transmission medium, and share a sixth optical mode coupler that combines and branches light at the other end of the optical transmission medium; The forward Mach-Zehnder interferometer comprises: At one end of the optical transmission medium, a forward measurement light source that emits light; a forward direction measurement light receiver that receives light from the third optical transmission line, said fifth optical mode coupler keeps a part of the fundamental mode light from said forward direction measurement light source as the fundamental mode and converts the remainder into a higher order mode, combines the light kept in the fundamental mode with the converted higher order mode light, and inputs the combined light into said first optical transmission path; At the other end of the optical transmission medium, the sixth optical mode coupler, among the light propagating through the first optical transmission line, leaves the light in fundamental mode as it is, converts the light in higher-order modes to fundamental mode, combines the light that remains in the fundamental mode with the converted light in fundamental mode, and outputs the combined light to the third optical transmission line; The reverse Mach-Zehnder interferometer comprises: At one end of the optical transmission medium, a backward direction measurement light source that transmits light of a wavelength different from that of the forward direction measurement light source to the fourth optical transmission line; a backward direction measurement optical receiver that receives light from the fifth optical mode coupler, the fifth optical mode coupler, among the light propagating through the first optical transmission line, leaves the light in fundamental mode as it is, converts the light in higher-order modes to fundamental mode, combines the light that remains in the fundamental mode with the converted light in fundamental mode, and outputs the combined light to the backward direction measurement light source; At the other end of the optical transmission medium, The sixth optical mode coupler keeps a part of the fundamental mode light from the fourth optical transmission line as the fundamental mode and converts the remainder into a higher-order mode, combines the light kept in the fundamental mode with the converted higher-order mode light, and inputs the combined light into the first optical transmission line. It is characterized by:

[0017] Specifically, the optical fiber vibration sensing device of the present disclosure comprises: a first AD converter that performs AD conversion on an electrical signal from the forward Mach-Zehnder interferometer; a second AD converter that converts an electrical signal from the reverse Mach-Zehnder interferometer into an AD converter; an analysis device that identifies a location where vibration occurs using the signal from the first AD converter and the signal from the second AD converter; The present invention is characterized by further comprising:

[0018] Specifically, the optical fiber vibration sensing device of the present disclosure comprises: a first AD converter that converts an electrical signal from the forward direction measurement light receiver into an AD signal; a second AD converter that converts an electrical signal from the reverse direction measurement light receiver into an AD signal; an analysis device that identifies a location where vibration occurs using the signal from the first AD converter and the signal from the second AD converter; The present invention is characterized by further comprising:

[0019] Specifically, the optical fiber vibration sensing method of the present disclosure includes: a fixed-time data acquisition step of acquiring interference wave signals w1(t) and w2(t) from a forward Mach-Zehnder interferometer and a backward Mach-Zehnder interferometer in which the light travels in the opposite direction to that of the forward Mach-Zehnder interferometer, respectively; A cross-correlation calculation step of changing τ in formula (8) and determining τ when the correlation value (w1 * w2) (τ) is maximized as ΔT; (w1*w2)(τ) = Σ w1(t)×w2(τ-t) (8) a vibration generation position calculation step of calculating a distance Lv from the other end of the optical transmission line to the point where the vibration is applied using equation (4); Lv = (L-c2×ΔT)c1 / (c1+c2) (4) where L is the total length of the optical transmission medium having multiple optical transmission paths. c1 is the speed of light in the optical transmission line of the forward Mach-Zehnder interferometer c2 is the speed of light in the optical transmission line of the reverse Mach-Zehnder interferometer Equipped with. Effect of the Invention

[0020] The optical fiber vibration sensing device and optical fiber vibration sensing method disclosed herein can realize optical fiber vibration sensing capable of identifying the position where vibration is applied with a simple configuration. [Brief description of the drawings]

[0021] [Figure 1] 1 is a diagram showing an example of the configuration of an optical fiber vibration sensing device according to the present disclosure. [Diagram 2] 1 is a diagram showing an example of the configuration of an optical fiber vibration sensing device according to the present disclosure. [Diagram 3] 1 is a diagram showing an example of the configuration of an optical fiber vibration sensing device according to the present disclosure. [Figure 4] 1 is a diagram showing an example of the configuration of an optical fiber vibration sensing device according to the present disclosure. [Diagram 5] 1 is a diagram showing an example of the configuration of an optical fiber vibration sensing device according to the present disclosure. [Figure 6] FIG. 2 is a diagram showing an example of processing of the optical fiber vibration sensing method of the present disclosure. [Figure 7] 1 is a diagram illustrating an example of a configuration of an optical mode coupler according to the present disclosure. [Figure 8] 1 is a diagram illustrating an example of a configuration of an optical mode coupler according to the present disclosure. [Figure 9] 1 is a diagram illustrating an example of a configuration of an optical mode coupler according to the present disclosure. [Figure 10] 1 is a diagram illustrating an example of a configuration of an optical mode coupler according to the present disclosure. [Figure 11] 1 is a diagram illustrating an example of a configuration of an optical mode coupler according to the present disclosure. [Figure 12] 1 is a diagram illustrating an example of a configuration of an optical mode coupler according to the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] Hereinafter, the embodiments of the present disclosure will be described in detail with reference to the drawings. Note that the present disclosure is not limited to the embodiments shown below. These implementation examples are merely illustrative, and the present disclosure can be implemented in various forms with various modifications and improvements based on the knowledge of those skilled in the art. Note that components with the same reference numerals in this specification and drawings are assumed to indicate the same components.

[0023] (Embodiment of Basic Configuration) The configuration of the optical fiber vibration sensing device of this embodiment is shown in Fig. 1. In Fig. 1, 1 is an optical transmission medium having a plurality of optical transmission paths, 10 is a forward Mach-Zehnder interferometer, and 11 is a backward Mach-Zehnder interferometer.

[0024] Examples include a multi-core optical fiber cable or a ribbon-type optical fiber cable having multiple optical fibers as the optical transmission medium, with multiple optical fibers as the multiple optical transmission paths, and a multi-core optical fiber or a multi-core optical fiber cable having multiple cores as the multiple optical transmission paths, with the cores of a multi-core optical fiber having multiple cores as the multiple optical transmission paths, with the optical transmission medium being a multi-core optical fiber or a multi-core optical fiber cable.

[0025] In the forward Mach-Zehnder interferometer 10, at one end of the optical transmission medium 1 having a plurality of optical transmission paths, a portion of the light in the fundamental mode is left in the fundamental mode and the remainder is converted to a higher-order mode, the light kept in the fundamental mode is combined with the converted light in the higher-order mode and input into the optical transmission path, and at the other end of the optical transmission medium 1 having a plurality of optical transmission paths, the light in the fundamental mode among the light propagated through the optical transmission paths is left in the fundamental mode and the light in the higher-order mode is converted to the fundamental mode, and the light kept in the fundamental mode is combined with the converted light in the fundamental mode for reception. In the backward Mach-Zehnder interferometer 11, at the other end of the optical transmission medium 1 having a plurality of optical transmission paths, a portion of the light in the fundamental mode is left as the fundamental mode and the remainder is converted to a higher mode, the light left as the fundamental mode and the converted light in the higher mode are combined and input to another optical transmission path, and at one end of the optical transmission medium 1 having a plurality of optical transmission paths, the light in the fundamental mode among the light propagating through the other optical transmission path is left as the fundamental mode and the light in the higher mode is converted to the fundamental mode, and the light left as the fundamental mode and the converted light in the fundamental mode are combined and received. The forward Mach-Zehnder interferometer 10 and the backward Mach-Zehnder interferometer 11 have the traveling directions of light set to opposite directions.

[0026] Each of the optical transmission lines has a propagation constant that allows light of a higher order mode to propagate at the wavelength of light used by the forward Mach-Zehnder interferometer 10 and the backward Mach-Zehnder interferometer 11 .

[0027] In FIG. 1, when vibration is applied to an optical transmission medium 1 having a plurality of optical transmission paths, a corresponding vibration is also applied to the optical transmission paths constituting a forward Mach-Zehnder interferometer 10 and the optical transmission paths constituting a reverse Mach-Zehnder interferometer 11. The vibration keeps the electric field distribution of the fundamental mode light constant, but changes the electric field distribution of the higher-order mode light. When the electric field distribution changes, the conversion efficiency changes when the higher-order mode light, which has propagated through the optical transmission path, is converted to the fundamental mode. The fundamental mode light remains in the fundamental mode, and the higher-order mode light is converted to the fundamental mode, and when the light that remained in the fundamental mode is combined with the converted fundamental mode light, a beat is generated.

[0028] From this, the forward Mach-Zehnder interferometer can observe an interference wave with a beat corresponding to the point Pv where the vibration is applied. Similarly, the backward Mach-Zehnder interferometer can observe an interference wave with a beat corresponding to the point Pv where the vibration is applied.

[0029] The optical fiber vibration sensing device of this embodiment may further include a first AD converter that performs AD conversion on the electric signal from the forward Mach-Zehnder interferometer, a second AD converter that performs AD conversion on the electric signal from the backward Mach-Zehnder interferometer, and an analyzer that identifies the location of vibration generation using the signal from the first AD converter and the signal from the second AD converter. The beat-containing interference waves observed by the forward Mach-Zehnder interferometer and the backward Mach-Zehnder interferometer are input to the analyzer via the first AD converter and the second AD converter, respectively, and the analyzer identifies the location of vibration generation.

[0030] (Application embodiment 1) The configuration of the optical fiber vibration sensing device of this embodiment is shown in Fig. 2. In Fig. 2, 1 is an optical transmission medium having a plurality of optical transmission paths, 20 is a first optical transmission path, 21 is a second optical transmission path, 100 is a light source for forward direction measurement, 101 is a light source for backward direction measurement, 200 is a light receiver for forward direction measurement, 201 is a light receiver for backward direction measurement, 300 is a first optical mode coupler, 310 is a second optical mode coupler, 301 is a third optical mode coupler, 311 is a fourth optical mode coupler, 400 is a first AD converter, 401 is a second AD converter, and 500 is an analysis device.

[0031] The optical fiber vibration sensing device includes a forward Mach-Zehnder interferometer and a reverse Mach-Zehnder interferometer, the light of which travels in opposite directions.

[0032] The forward Mach-Zehnder interferometer is provided at one end of an optical transmission medium 1 having a plurality of optical transmission paths with a forward measurement light source 100 for sending out light, and a first optical mode coupler 300 for leaving part of the fundamental mode light from the forward measurement light source 100 in the fundamental mode and converting the remainder to a higher mode, combining the light kept in the fundamental mode with the converted light in the higher mode, and inputting the combined light to a first optical transmission path 20. At the other end of the optical transmission medium 1 having a plurality of optical transmission paths with a second optical mode coupler 310 for leaving the fundamental mode light of the light propagating through the first optical transmission path 20 in the fundamental mode and converting the higher mode light to the fundamental mode, combining the light kept in the fundamental mode with the converted light in the fundamental mode, and a forward measurement optical receiver 200 for receiving light from the second optical mode coupler 310.

[0033] In the forward Mach-Zehnder interferometer, a forward measurement light source 100 at one end of an optical transmission medium 1 having a plurality of optical transmission paths transmits light, and a first optical mode coupler 300 leaves part of the fundamental mode light from the forward measurement light source 100 in the fundamental mode and converts the remainder to a higher-order mode, combines the light that has been kept in the fundamental mode with the converted light in the higher-order mode, and inputs it to a first optical transmission path 20. A second optical mode coupler 310 at the other end of the optical transmission medium 1 having a plurality of optical transmission paths leaves the fundamental mode light of the light that has propagated through the first optical transmission path 20 in the fundamental mode and converts the higher-order mode light to the fundamental mode, combines the light that has been kept in the fundamental mode with the converted light in the fundamental mode, and a forward measurement optical receiver 200 receives the light from the second optical mode coupler 310.

[0034] The backward Mach-Zehnder interferometer includes a backward measurement light source 101 that transmits light at the other end of an optical transmission medium 1 having a plurality of optical transmission paths, and a third optical mode coupler 301 that keeps a part of the fundamental mode light from the backward measurement light source 101 as the fundamental mode and converts the remainder to a higher mode, combines the light that remains in the fundamental mode with the converted light in the higher mode, and inputs the combined light to a second optical transmission path 21. The backward measurement optical receiver 201 that receives light from the fourth optical mode coupler 311 is provided at one end of the optical transmission medium 1 having a plurality of optical transmission paths, keeps the light in the fundamental mode as the fundamental mode and converts the light in the higher mode to the fundamental mode, and combines the light that remains in the fundamental mode with the converted light in the fundamental mode.

[0035] In the backward Mach-Zehnder interferometer, a backward measurement light source 101 at the other end of an optical transmission medium 1 having a plurality of optical transmission paths transmits light, and a third optical mode coupler 301 keeps part of the fundamental mode light from the backward measurement light source 101 in the fundamental mode and converts the rest to a higher mode, combines the light kept in the fundamental mode with the converted light in the higher mode, and inputs it to a second optical transmission path 21. A fourth optical mode coupler 311 at one end of the optical transmission medium 1 having a plurality of optical transmission paths keeps the fundamental mode light of the light propagating through the second optical transmission path 21 in the fundamental mode and converts the higher mode light to the fundamental mode, combines the light kept in the fundamental mode with the converted light in the fundamental mode, and a backward measurement optical receiver 201 receives the light from the fourth optical mode coupler 311.

[0036] An example of the configuration of the first optical mode coupler 300 is shown in FIG. 7. In FIG. 7, the first optical mode coupler 300 is composed of an optical branching / coupling coupler 300-1 and an optical mode conversion coupler 300-2. The optical branching / coupling coupler 300-1 branches the fundamental mode light input to one input terminal into two fundamental mode lights. The optical mode conversion coupler 300-2 keeps the fundamental mode light input to one input terminal as it is, converts the fundamental mode light input to the other input terminal into a higher mode light, and combines and outputs the light kept in the fundamental mode and the converted higher mode light. The optical mode conversion coupler is described in detail in Non-Patent Document 3. A similar configuration can be exemplified for the third optical mode coupler 301. The same applies to the following application embodiments.

[0037] Another example of the configuration of the first optical mode coupler 300 is shown in FIG. 11. In FIG. 11, 300-3 is an axis-offset connection part. In the axis-offset connection part 300-3, two optical fibers are connected with the centers of the cores offset. The axis-offset connection part 300-3 may be fabricated by welding the centers of the cores of the two optical fibers offset in the direction of the axis, or by connecting them with a connector. Due to the axial discontinuity of the cores of the two optical fibers, the light propagating in the fundamental mode is coupled to the guided mode of the fundamental mode and the higher mode. With this configuration, an inexpensive optical mode coupler can be obtained. It is desirable that the optical fiber on the side of the forward measurement light source 100 of the axis-offset connection part 300-3 is an optical fiber that propagates only in the fundamental mode. A highly accurate optical fiber vibration sensing device can be obtained. A similar configuration can be illustrated for the third optical mode coupler 301. The same applies to the following application embodiments.

[0038] An example of the configuration of the second optical mode coupler 310 is shown in FIG. 8. In FIG. 8, the second optical mode coupler 310 is composed of an optical mode conversion coupler 300-2 and an optical branching and coupling coupler 300-1. The optical mode conversion coupler 300-2 here is an inverse of the input / output relationship of the optical mode conversion coupler 300-2 in the first optical mode coupler 300. That is, the optical mode conversion coupler 300-2 outputs the fundamental mode light of the light input to one input terminal to one output terminal while keeping it in the fundamental mode, and converts the light of the higher order mode to the fundamental mode and outputs it to the other output terminal. The optical branching and coupling coupler 300-1 here is an inverse of the input / output relationship of the optical branching and coupling coupler 300-1 in the first optical mode coupler 300. That is, the optical branching and coupling coupler 300-1 couples the fundamental mode light input to one input terminal with the fundamental mode light input to the other input terminal, and outputs the fundamental mode light to the output terminal. The optical mode conversion coupler is described in detail in Non-Patent Document 3. A similar configuration can be exemplified for the fourth optical mode coupler 311. The same applies to the following application embodiments.

[0039] Another example of the configuration of the second optical mode coupler 310 is shown in FIG. 12. In FIG. 12, 300-3 is an axially offset connection part, and 300-4 is a single mode optical fiber. In the axially offset connection part 300-3, two optical fibers are connected with their core centers offset. The axially offset connection part 300-3 may be fused with the centers of the cores of the two optical fibers offset, or may be fabricated by connecting them with a connector. The single mode optical fiber 300-4 is an optical fiber that propagates only the fundamental mode at the wavelength of the light emitted by the forward measurement light source 100. Due to the axial discontinuity of the cores of the two optical fibers, the light propagating in the fundamental mode couples with the guided modes of the fundamental mode and the higher order mode, and the light propagating in the higher order mode couples with the guided modes of the fundamental mode and the higher order mode. Among them, the single mode optical fiber 300-4 selects and propagates only the fundamental mode. That is, the optical mode coupler in Fig. 12 leaves part of the fundamental mode light of the light input to the input terminal as it is, and converts part of the higher mode light to the fundamental mode and outputs it. With this configuration, it is possible to make an inexpensive optical mode coupler. A similar configuration can be exemplified for the fourth optical mode coupler 311. The same applies to the following application embodiments.

[0040] The first optical transmission line 20 has a propagation constant that allows light of a higher order mode to propagate at the wavelength of light emitted by the forward direction measurement light source 100. The second optical transmission line 21 has a propagation constant that allows light of a higher order mode to propagate at the wavelength of light emitted by the backward direction measurement light source 101.

[0041] The optical fiber vibration sensing device of the present disclosure can realize optical fiber vibration sensing capable of identifying the position where vibration is applied with a simple configuration.

[0042] (Application embodiment 2) The configuration of the optical fiber vibration sensing device of this embodiment is shown in Fig. 3. In Fig. 3, 1 is an optical transmission medium having a plurality of optical transmission paths, 20 is a first optical transmission path, 21 is a second optical transmission path, 40 is a third optical transmission path, 41 is a fourth optical transmission path, 100 is a light source for forward direction measurement, 101 is a light source for backward direction measurement, 200 is a light receiver for forward direction measurement, 201 is a light receiver for backward direction measurement, 300 is a first optical mode coupler, 310 is a second optical mode coupler, 301 is a third optical mode coupler, 311 is a fourth optical mode coupler, 400 is a first AD converter, 401 is a second AD converter, and 500 is an analysis device.

[0043] The optical fiber vibration sensing device includes a forward direction Mach-Zehnder interferometer and a backward direction Mach-Zehnder interferometer, each of which has its light travelling in the opposite direction. The basic operating principle is the same as in Application Example 1, but differs from Application Example 1 in that the forward direction measurement photoreceiver 200 of the forward direction Mach-Zehnder interferometer and the backward direction measurement light source 101 of the backward direction Mach-Zehnder interferometer are disposed at one end of an optical transmission medium 1 having a plurality of optical transmission paths.

[0044] The forward Mach-Zehnder interferometer is provided at one end of an optical transmission medium 1 having a plurality of optical transmission paths with a forward measurement light source 100 for transmitting light, a first optical mode coupler 300 for leaving a portion of the fundamental mode light from the forward measurement light source 100 in the fundamental mode and converting the remainder to a higher mode, combining the light kept in the fundamental mode with the converted light in the higher mode, and inputting the combined light to a first optical transmission path 20, and a forward measurement optical receiver 200 for receiving light from a third optical transmission path 40. At the other end of the optical transmission medium 1 having a plurality of optical transmission paths with a second optical mode coupler 310 for leaving the fundamental mode light of the light propagating through the first optical transmission path 20 in the fundamental mode and converting the higher mode light to the fundamental mode, combining the light kept in the fundamental mode with the converted light in the fundamental mode, and outputting the combined light to the third optical transmission path 40.

[0045] In the forward Mach-Zehnder interferometer, a forward measurement light source 100 at one end of an optical transmission medium 1 having a plurality of optical transmission paths transmits light, and a first optical mode coupler 300 leaves part of the fundamental mode light from the forward measurement light source 100 in the fundamental mode and converts the rest to a higher mode, combines the fundamental mode light with the converted higher mode light, and inputs it to a first optical transmission path 20. A second optical mode coupler 310 at the other end of the optical transmission medium 1 having a plurality of optical transmission paths leaves the fundamental mode light of the light propagating through the first optical transmission path 20 in the fundamental mode and converts the higher mode light to the fundamental mode, combines the fundamental mode light with the converted fundamental mode light, and outputs it to a third optical transmission path 40. A forward measurement optical receiver 200 at one end of the optical transmission medium 1 having a plurality of optical transmission paths receives light from the third optical transmission path 40.

[0046] The backward Mach-Zehnder interferometer includes, at one end of an optical transmission medium 1 having a plurality of optical transmission paths, a backward measurement light source 101 that transmits light to a fourth optical transmission path 41, a fourth optical mode coupler 311 that, among the light propagating through the second optical transmission path 21, leaves the light in fundamental mode as it is and converts the light in higher-order modes to fundamental mode, and couples the light in the fundamental mode with the converted light in the fundamental mode, and a backward measurement optical receiver 201 that receives the light from the fourth optical mode coupler 311. At the other end of the optical transmission medium 1 having a plurality of optical transmission paths, there is a third optical mode coupler 301 that leaves a part of the light in fundamental mode from the fourth optical transmission path 41 as it is in fundamental mode, converts the rest to a higher-order mode, combines the light in the fundamental mode with the converted light in the higher-order mode, and inputs the combined light to the second optical transmission path 21.

[0047] In the backward Mach-Zehnder interferometer, a backward measurement light source 101 at one end of an optical transmission medium 1 having a plurality of optical transmission lines sends light to a fourth optical transmission line 41. A third optical mode coupler 301 at the other end of the optical transmission medium 1 having a plurality of optical transmission lines keeps a part of the fundamental mode light propagating through the fourth optical transmission line 41 as the fundamental mode and converts the rest to a higher-order mode, combines the light that has been kept in the fundamental mode with the converted light in the higher-order mode, and inputs it to a second optical transmission line 21. A fourth optical mode coupler 311 at one end of the optical transmission medium 1 having a plurality of optical transmission lines keeps the fundamental mode light of the light that has propagated through the second optical transmission line 21 as the fundamental mode and converts the light in the higher-order mode to the fundamental mode, combines the light that has been kept in the fundamental mode with the converted light in the fundamental mode, and a backward measurement optical receiver 201 receives the light from the fourth optical mode coupler 311.

[0048] The first optical transmission path 20 has a propagation constant that allows the propagation of higher-order mode light at the wavelength of light sent from the forward direction measurement light source 100. The third optical transmission path 40 has a propagation constant that allows only fundamental mode light or higher-order mode light to propagate at the wavelength of light sent from the forward direction measurement light source 100. The second optical transmission path 21 has a propagation constant that allows higher-order mode light to propagate at the wavelength of light sent from the backward direction measurement light source 101. The fourth optical transmission path 41 has a propagation constant that allows only fundamental mode light or higher-order mode light to propagate at the wavelength of light sent from the backward direction measurement light source 101.

[0049] The optical fiber vibration sensing device of the present disclosure can realize optical fiber vibration sensing capable of identifying the position where vibration is applied with a simple configuration. Also, the optical fiber vibration sensing device of the present disclosure can arrange the forward direction measurement light source 100, the backward direction measurement light source 101, the forward direction measurement optical receiver 200, and the backward direction measurement optical receiver 201, which are active devices, on the same side (one end of the optical transmission medium 1 having multiple optical transmission paths).

[0050] (Application embodiment 3) The configuration of the optical fiber vibration sensing device of this embodiment is shown in Fig. 4. In Fig. 4, 1 is an optical transmission medium having a plurality of optical transmission paths, 20 is a first optical transmission path, 21 is a second optical transmission path, 100 is a forward direction measurement light source, 101 is a backward direction measurement light source, 200 is a forward direction measurement light receiver, 201 is a backward direction measurement light receiver, 320 is a fifth optical mode coupler, 330 is a sixth optical mode coupler, 400 is a first AD converter, 401 is a second AD converter, and 500 is an analysis device. In this application embodiment, different optical transmission paths are secured for a single optical fiber in the forward direction Mach-Zehnder interferometer and the backward direction Mach-Zehnder interferometer by wavelength division multiplexing technology.

[0051] The optical fiber vibration sensing device includes a forward Mach-Zehnder interferometer and a backward Mach-Zehnder interferometer, each of which has its light traveling in the opposite direction. The basic operating principle is the same as in Application Example 1, but it differs from Application Example 1 in that the forward Mach-Zehnder interferometer and the backward Mach-Zehnder interferometer share the same optical fiber by using different wavelengths for the forward measurement light source 100 of the forward Mach-Zehnder interferometer and the backward measurement light source 101 of the backward Mach-Zehnder interferometer.

[0052] The forward Mach-Zehnder interferometer and the reverse Mach-Zehnder interferometer share a fifth optical mode coupler 320 that is connected to a first optical transmission path 20 and a second optical transmission path 21 and that couples / branches light at one end of the optical transmission medium 1 having a plurality of optical transmission paths, and share a sixth optical mode coupler 330 that is connected to the first optical transmission path 20 and the second optical transmission path 21 and that couples / branches light at the other end of the optical transmission medium 1 having a plurality of optical transmission paths.

[0053] The forward direction Mach-Zehnder interferometer includes a forward direction measurement light source 100 that transmits light at one end of an optical transmission medium 1 having a plurality of optical transmission paths, a fifth optical mode coupler 320 that keeps a part of the fundamental mode light from the forward direction measurement light source 100 as the fundamental mode and converts the rest to a higher mode, combines the light that has been kept in the fundamental mode with the converted light in the higher mode, and inputs the combined light to a first optical transmission path 20. The other end of the optical transmission medium 1 having a plurality of optical transmission paths includes a sixth optical mode coupler 330 that keeps the fundamental mode light of the light propagating through the first optical transmission path 20 as the fundamental mode and converts the higher mode light to the fundamental mode, combines the light that has been kept in the fundamental mode with the converted light in the fundamental mode, and outputs the combined light to a forward direction measurement optical receiver 200, and a forward direction measurement optical receiver 200 that receives the light from the sixth optical mode coupler 330.

[0054] In the forward Mach-Zehnder interferometer, a forward measurement light source 100 at one end of an optical transmission medium 1 having a plurality of optical transmission paths transmits light, and a fifth optical mode coupler 320 keeps a part of the fundamental mode light from the forward measurement light source 100 in the fundamental mode and converts the rest to a higher mode, combines the light that has been kept in the fundamental mode with the converted light in the higher mode, and inputs it to a first optical transmission path 20. A sixth optical mode coupler 330 at the other end of the optical transmission medium 1 having a plurality of optical transmission paths keeps the fundamental mode light of the light that has propagated through the first optical transmission path 20 in the fundamental mode and converts the higher mode light to the fundamental mode, combines the light that has been kept in the fundamental mode with the converted light in the fundamental mode, and outputs it to a forward measurement optical receiver 200. The forward measurement optical receiver 200 receives the light from the sixth optical mode coupler 330.

[0055] The backward Mach-Zehnder interferometer includes a backward measurement light source 101 that transmits light of a wavelength different from that of the forward measurement light source 100 at the other end of the optical transmission medium 1 having a plurality of optical transmission paths, and a sixth optical mode coupler 330 that keeps a part of the fundamental mode light from the backward measurement light source 101 as the fundamental mode and converts the rest to a higher mode, combines the light that remains in the fundamental mode with the converted light in the higher mode, and inputs the combined light to the second optical transmission path 21. The optical transmission medium 1 having a plurality of optical transmission paths includes a fifth optical mode coupler 320 that keeps the fundamental mode light of the light propagating through the second optical transmission path 21 as the fundamental mode and converts the higher mode light to the fundamental mode, combines the light that remains in the fundamental mode with the converted light in the fundamental mode, and outputs the combined light to the backward measurement optical receiver 201, and a backward measurement optical receiver 201 that receives the light from the fifth optical mode coupler 320.

[0056] In the backward Mach-Zehnder interferometer, the backward measurement light source 101 at the other end of the optical transmission medium 1 having a plurality of optical transmission paths transmits light, and the sixth optical mode coupler 330 leaves part of the fundamental mode light from the backward measurement light source 101 as the fundamental mode and converts the rest to a higher mode, combines the light that has been kept in the fundamental mode with the converted light in the higher mode, and inputs it to the second optical transmission path 21. The fifth optical mode coupler 320 at one end of the optical transmission medium 1 having a plurality of optical transmission paths leaves the fundamental mode light of the light propagating through the second optical transmission path 21 as the fundamental mode and converts the higher mode light to the fundamental mode, combines the light that has been kept in the fundamental mode with the converted light in the fundamental mode, and outputs it to the backward measurement optical receiver 201. The backward measurement optical receiver 201 receives the light from the fifth optical mode coupler 320.

[0057] An example of the configuration of the fifth optical mode coupler 320 is shown in Fig. 9. In Fig. 9, the fifth optical mode coupler 320 is composed of an optical branching / coupling coupler 320-1 and an optical mode conversion coupler 320-2. The optical branching / coupling coupler 320-1 branches the fundamental mode light input to one input terminal on the left side of the drawing into two fundamental mode lights, branches the fundamental mode light input to the other input terminal on the left side of the drawing into two fundamental mode lights, and outputs the fundamental mode light input to one input terminal and the fundamental mode light input to the other input terminal to each output terminal on the right side of the drawing after multiplexing them. The reverse operation is performed for light from the right side of the drawing. That is, the optical branching / coupling coupler 320-1 branches the fundamental mode light inputted to one input terminal on the right side of the drawing into two fundamental mode lights, branches the fundamental mode light inputted to another input terminal on the right side of the drawing into two fundamental mode lights, and outputs the fundamental mode light inputted to one input terminal and the fundamental mode light inputted to the other input terminal to each output terminal on the left side of the drawing after multiplexing. The optical mode conversion coupler 300-2 keeps the fundamental mode light inputted to one input terminal on the left side of the drawing as it is, converts the fundamental mode light inputted to the other input terminal on the left side of the drawing into light of a higher order mode, multiplexes the light kept in the fundamental mode and the converted light of the higher order mode, and outputs it to the output terminal on the right side of the drawing. It operates in the opposite manner for light from the right side of the drawing. The optical mode conversion coupler 300-2 keeps the fundamental mode light inputted to one input terminal on the right side of the drawing as it is, and outputs it to one output terminal on the left side of the drawing. Higher-order mode light input to one input terminal on the right side of the drawing is converted to fundamental mode light and output to another output terminal on the left side of the drawing. Optical mode conversion couplers are described in detail in Non-Patent Document 3. The same applies to the following application embodiments.

[0058] An example of the configuration of the sixth optical mode coupler 330 is shown in Fig. 10. The sixth optical mode coupler shown in Fig. 10 operates in the same manner as the fifth optical mode coupler 320. The configuration is simply reversed on the left and right in the drawing. Optical mode conversion couplers are described in detail in Non-Patent Document 3. The same applies to the following application embodiments.

[0059] The first optical transmission line 20 has a propagation constant that allows light of a higher order mode to propagate at the wavelength of light emitted by the forward direction measurement light source 100. The second optical transmission line 21 has a propagation constant that allows light of a higher order mode to propagate at the wavelength of light emitted by the backward direction measurement light source 101.

[0060] The optical fiber vibration sensing device disclosed herein can realize optical fiber vibration sensing capable of identifying the position where vibration is applied with a simple configuration. Moreover, the optical fiber vibration sensing device disclosed herein can share the same optical fiber by using different wavelengths for the forward Mach-Zehnder interferometer and the reverse Mach-Zehnder interferometer.

[0061] (Application embodiment 4) The configuration of the optical fiber vibration sensing device of this embodiment is shown in Fig. 5. In Fig. 5, 1 is an optical transmission medium having a plurality of optical transmission paths, 20 is a first optical transmission path, 21 is a second optical transmission path, 40 is a third optical transmission path, 41 is a fourth optical transmission path, 100 is a forward direction measurement light source, 101 is a backward direction measurement light source, 200 is a forward direction measurement light receiver, 201 is a backward direction measurement light receiver, 320 is a fifth optical mode coupler, 330 is a sixth optical mode coupler, 400 is a first AD converter, 401 is a second AD converter, and 500 is an analysis device. In this application embodiment, different optical transmission paths are secured for a single optical fiber in the forward direction Mach-Zehnder interferometer and the backward direction Mach-Zehnder interferometer by wavelength division multiplexing technology.

[0062] The optical fiber vibration sensing device includes a forward Mach-Zehnder interferometer and a backward Mach-Zehnder interferometer, each of which has light traveling in the opposite directions. The basic operating principle is the same as that of the application embodiment 1, but differs from the application embodiment 1 in that the forward measurement light receiver 200 of the forward Mach-Zehnder interferometer and the backward measurement light source 101 of the backward Mach-Zehnder interferometer are disposed at one end of an optical transmission medium 1 having a plurality of optical transmission paths. Also, different wavelengths are used for the forward measurement light source 100 of the forward Mach-Zehnder interferometer and the backward measurement light source 101 of the backward Mach-Zehnder interferometer, so that the forward Mach-Zehnder interferometer and the backward Mach-Zehnder interferometer share the same optical fiber.

[0063] The forward Mach-Zehnder interferometer and the reverse Mach-Zehnder interferometer share a fifth optical mode coupler 320 that is connected to a first optical transmission path 20 and a second optical transmission path 21 and that couples / branches light at one end of the optical transmission medium 1 having a plurality of optical transmission paths, and share a sixth optical mode coupler 330 that is connected to the first optical transmission path 20 and the second optical transmission path 21 and that couples / branches light at the other end of the optical transmission medium 1 having a plurality of optical transmission paths.

[0064] The forward direction Mach-Zehnder interferometer includes a forward direction measurement light source 100 that transmits light at one end of an optical transmission medium 1 having a plurality of optical transmission paths, a fifth optical mode coupler 320 that keeps a part of the fundamental mode light from the forward direction measurement light source 100 in the fundamental mode and converts the rest to a higher mode, combines the light kept in the fundamental mode with the converted light in the higher mode, and inputs the combined light to the first optical transmission path 20, and a forward direction measurement optical receiver 200 that receives light from the third optical transmission path 40. The other end of the optical transmission medium 1 having a plurality of optical transmission paths includes a sixth optical mode coupler 330 that keeps the fundamental mode light of the light propagating through the first optical transmission path 20 in the fundamental mode and converts the higher mode light to the fundamental mode, combines the light kept in the fundamental mode with the converted light in the fundamental mode, and outputs the combined light to the third optical transmission path 40.

[0065] In the forward Mach-Zehnder interferometer, a forward measurement light source 100 at one end of an optical transmission medium 1 having a plurality of optical transmission paths transmits light, and a fifth optical mode coupler 320 keeps a part of the fundamental mode light from the forward measurement light source 100 in the fundamental mode and converts the rest to a higher mode, combines the light that has been kept in the fundamental mode with the converted light in the higher mode, and inputs it to a first optical transmission path 20. A sixth optical mode coupler 330 at the other end of the optical transmission medium 1 having a plurality of optical transmission paths keeps the fundamental mode light of the light that has propagated through the first optical transmission path 20 in the fundamental mode and converts the light in the higher mode to the fundamental mode, combines the light that has been kept in the fundamental mode with the converted light in the fundamental mode, and outputs it to a third optical transmission path 40. A forward measurement optical receiver 200 at one end of the optical transmission medium 1 having a plurality of optical transmission paths receives light from the third optical transmission path 40.

[0066] The backward Mach-Zehnder interferometer is provided with a backward measurement light source 101 at one end of an optical transmission medium 1 having a plurality of optical transmission paths, which transmits light having a wavelength different from that of the forward measurement light source 100 to a fourth optical transmission path 41, a fifth optical mode coupler 320 which, among the light propagating through the second optical transmission path 21, leaves the light in fundamental mode as it is and converts the light in higher order modes to fundamental mode, combines the light in the fundamental mode with the converted light in the fundamental mode, and outputs the combined light to a backward measurement optical receiver 201, and a backward measurement optical receiver 201 which receives the light from the fifth optical mode coupler 320. The other end of the optical transmission medium 1 having a plurality of optical transmission paths is provided with a sixth optical mode coupler 330 which leaves a part of the light in fundamental mode from the fourth optical transmission path 41 as it is in fundamental mode, converts the rest to a higher order mode, combines the light in the fundamental mode with the converted light in the higher order mode, and inputs the combined light to the second optical transmission path 21.

[0067] In the backward Mach-Zehnder interferometer, a backward measurement light source 101 at one end of an optical transmission medium 1 having a plurality of optical transmission lines sends light to a fourth optical transmission line 41. A sixth optical mode coupler 330 at the other end of the optical transmission medium 1 having a plurality of optical transmission lines keeps a part of the fundamental mode light propagating through the fourth optical transmission line 41 as the fundamental mode and converts the rest to a higher-order mode, combines the light that has been kept in the fundamental mode with the converted light in the higher-order mode, and inputs it to a second optical transmission line 21. A fifth optical mode coupler 320 at one end of the optical transmission medium 1 having a plurality of optical transmission lines keeps the fundamental mode light of the light that has propagated through the second optical transmission line 21 as the fundamental mode and converts the light in the higher-order mode to the fundamental mode, combines the light that has been kept in the fundamental mode with the converted light in the fundamental mode, and outputs it to a backward measurement optical receiver 201. The backward measurement optical receiver 201 receives the light from the fifth optical mode coupler 320.

[0068] The first optical transmission path 20 has a propagation constant that allows the propagation of higher-order mode light at the wavelength of light sent from the forward direction measurement light source 100. The third optical transmission path 40 has a propagation constant that allows only fundamental mode light or higher-order mode light to propagate at the wavelength of light sent from the forward direction measurement light source 100. The second optical transmission path 21 has a propagation constant that allows higher-order mode light to propagate at the wavelength of light sent from the backward direction measurement light source 101. The fourth optical transmission path 41 has a propagation constant that allows only fundamental mode light or higher-order mode light to propagate at the wavelength of light sent from the backward direction measurement light source 101.

[0069] The optical fiber vibration sensing device of the present disclosure can realize optical fiber vibration sensing capable of identifying the position where vibration is applied with a simple configuration. Moreover, the optical fiber vibration sensing device of the present disclosure can arrange the forward direction measurement light source 100, the backward direction measurement light source 101, the forward direction measurement receiver 200, and the backward direction measurement receiver 201, which are active devices, on the same side (one end of the optical transmission medium 1 having a plurality of optical transmission paths). Furthermore, the optical fiber vibration sensing device of the present disclosure can share the same optical fiber by using different wavelengths for the forward direction Mach-Zehnder interferometer and the backward direction Mach-Zehnder interferometer.

[0070] (Application embodiment 5) In the basic configuration embodiment and application embodiments 1 to 4, the optical fiber vibration sensing device may further include a first AD converter 400 that performs AD conversion of an electrical signal from a forward direction Mach-Zehnder interferometer (in application embodiments 1 to 4, the forward direction measurement receiver 200), a second AD converter 401 that performs AD conversion of an electrical signal from a reverse direction Mach-Zehnder interferometer (in application embodiments 1 to 4, the reverse direction measurement receiver 201), and an analysis device 500 that identifies the location of the vibration using the signal from the first AD converter 400 and the signal from the second AD converter 401.

[0071] In FIG. 1, if the total length of the optical transmission medium 1 having a plurality of optical transmission paths is L, and the distance from the other end of the optical transmission path to the point Pv where the vibration is added is Lv, the time T1 required for the beat interference wave caused by the vibration added at the point Pv to reach the other end of the optical transmission path of the forward Mach-Zehnder interferometer is given by: T1 = Lv / c1 (1) Here, c1 is the speed of light in the optical transmission line of the forward Mach-Zehnder interferometer.

[0072] The time T2 required for the beat-containing interference wave caused by the vibration added at point Pv to reach one end of the optical transmission line of the reverse Mach-Zehnder interferometer is given by T2 = (L-Lv) / c2 (2) Here, c2 is the speed of light in the optical transmission line of the reverse Mach-Zehnder interferometer.

[0073] As a result, the time difference ΔT between when the beat-containing interference wave caused by the vibration added at point Pv reaches the other end of the optical transmission line of the forward Mach-Zehnder interferometer and when it reaches one end of the optical transmission line of the backward Mach-Zehnder interferometer is ΔT = T2-T1 = (L-Lv) / c2-Lv / c1 (3) From this, the distance Lv from the other end of the optical transmission line to the point Pv where the vibration is applied can be obtained by equation (4). Lv = (L-c2×ΔT)c1 / (c1+c2) (4)

[0074] If the speed of light in the optical transmission path of both the forward and reverse Mach-Zehnder interferometers is c, then equation (4) becomes Lv = (Lc × ΔT) / 2 (5) For example, when the vibration application point Pv is at the midpoint of the optical transmission medium 1 having a plurality of optical transmission paths, ΔT = 0 (6) Equation (5) is Lv = L / 2 (7) From equation (7), the point Pv where the vibration is applied is located halfway through the optical transmission medium 1 having multiple optical transmission paths, and so the validity of equation (4) is demonstrated.

[0075] In this way, by measuring the time difference ΔT between when the beat interference wave caused by the vibration added at point Pv reaches the other end of the optical transmission path of the forward Mach-Zehnder interferometer and when it reaches one end of the optical transmission path of the reverse Mach-Zehnder interferometer, it is possible to obtain the distance Lv from the other end of the optical transmission path of the forward Mach-Zehnder interferometer to the point Pv where the vibration is added. Note that a beat interference wave is generated only when two lights are combined, but for convenience, the explanation here is given assuming that the beat interference wave propagates from the point where the vibration is added.

[0076] The two interference wave signals observed at the same time by the forward direction measurement receiver 200 and the reverse direction measurement receiver 201 are denoted as w1(t) and w2(t). ΔT is equal to the shift amount when the cross-correlation value of w1(t) and w2(t) is at its maximum. In other words, it can be found by changing τ in the following equation and setting τ at the time when the correlation value (w1*w2)(τ) is at its maximum as ΔT. (w1*w2)(τ) = Σ w1(t)×w2(τ-t) (8)

[0077] The analysis device 500 takes in the interference wave signal through the first AD converter 400 and the second AD converter 401, calculates the cross-correlation at regular time intervals, and obtains ΔT, thereby making it possible to specify the distance Lv to the vibration occurrence position Pv. Thus, the points where vibration is applied can be obtained sequentially.

[0078] The analysis device 500 identifies the location of the vibration occurrence in consideration of the delay time of the optical signal from the other end of the optical transmission path to the forward direction measurement receiver 200, the delay time of the electrical signal from the forward direction measurement receiver 200 via the first AD converter 400 to the analysis device 500, the delay time of the optical signal from one end of the optical transmission path to the reverse direction measurement receiver 201, and the delay time of the electrical signal from the reverse direction measurement receiver 201 to the analysis device 500 via the second AD converter 401.

[0079] 6 shows a flowchart of the optical fiber position sensing method executed by the analysis device 500. In the fixed time data acquisition process 600, interference wave signals w1(t) and w2(t) are acquired from a forward direction Mach-Zehnder interferometer (forward direction measurement receiver 200 in application embodiments 1 to 4) and a backward direction Mach-Zehnder interferometer (for backward direction measurement receiver 201 in application embodiments 1 to 4) in which the light travels in the opposite direction to that of the forward direction Mach-Zehnder interferometer, respectively.

[0080] In the cross-correlation calculation step 601, τ in the formula (8) is changed, and τ when the correlation value (w1*w2)(τ) is maximized is obtained as ΔT. (w1*w2)(τ) = Σ w1(t)×w2(τ-t) (8)

[0081] In the vibration occurrence position calculation step 603, the distance Lv from the other end of the optical transmission line to the point where the vibration is applied is calculated using equation (4). Lv = (L-c2×ΔT)c1 / (c1+c2) (4) Here, L is the total length of the optical transmission medium having a plurality of optical transmission lines, c1 is the speed of light in the optical transmission line of the directional Mach-Zehnder interferometer, and c2 is the speed of light in the optical transmission line of the reverse Mach-Zehnder interferometer.

[0082] An effective time difference calculation step 602 may be provided between the cross-correlation calculation step 601 and the vibration occurrence position calculation step 603. The interference signals received by the forward direction measurement receiver 200 and the reverse direction measurement receiver 201 may have a poor signal-to-noise ratio (SNR) depending on the interference state, and may not be an effective time difference ΔT. Therefore, in the effective time difference calculation step 602, the maximum time difference ΔTmax expected from the longest distance L of the optical transmission medium 1 having multiple optical transmission paths is compared with the absolute value of ΔT, |ΔT| ≦ ΔTmax (9) If not, the process returns to the data acquisition step 600 for a certain period of time and starts over from data acquisition. Here, ΔTmax is obtained by the following formula. ΔTmax = max{L / c1,L / c2} (10) If the formula (9) is satisfied, the process proceeds to vibration occurrence position calculation step 603 .

[0083] As described above, the optical fiber vibration sensing device and optical fiber vibration sensing method disclosed herein can realize optical fiber vibration sensing that can identify the position where vibration is applied, with a simple configuration.

[0084] The analysis device of the present invention can also be realized by a computer and a program. The program can be recorded on a recording medium or provided via a communication network. [Industrial Applicability]

[0085] The present disclosure can be applied to the information and communications industry. [Explanation of symbols]

[0086] 1: Optical transmission medium having multiple optical transmission paths 10: Forward Mach-Zehnder interferometer 11: Reverse Mach-Zehnder interferometer 20: First optical transmission path 21: Second optical transmission path 40: Third optical transmission path 41: Fourth optical transmission line 100: Forward measurement light source 101: Light source for reverse measurement 200: Forward measurement receiver 201: Reverse direction measurement receiver 300: First optical mode coupler 300-1: Optical branching coupler 300-2: Optical mode conversion coupler 300-3: Off-axis connection 300-4: Single mode optical fiber 310: Second optical mode coupler 301: Third optical mode coupler 311: 4th optical mode coupler 320: 5th optical mode coupler 320-1: Optical branching coupler 320-2: Optical mode conversion coupler 330: 6th optical mode coupler 400: First AD converter 401: Second AD converter 500: Analysis device

Claims

1. an optical transmission medium having a plurality of optical transmission paths; a forward Mach-Zehnder interferometer which, at one end of the optical transmission medium, leaves a portion of the light in fundamental mode as it is and converts the remainder to a higher-order mode, combines the light left in fundamental mode with the converted light in higher-order mode, and inputs the combined light into an optical transmission line, and at the other end of the optical transmission medium, leaves the light in fundamental mode of the light that has propagated through the optical transmission line in fundamental mode and converts the light in higher-order mode to fundamental mode, and combines and receives the light left in fundamental mode with the converted light in fundamental mode; a reverse Mach-Zehnder interferometer which, at the other end of the optical transmission medium, leaves a part of the light in fundamental mode as it is and converts the remainder to a higher-order mode, combines the light left in fundamental mode with the converted light in higher-order mode, and inputs the combined light to another optical transmission path, and at one end of the optical transmission medium, leaves the light in fundamental mode of the light propagating through the other optical transmission path in fundamental mode and converts the light in higher-order mode to fundamental mode, and combines and receives the light left in fundamental mode with the converted light in fundamental mode; An optical fiber vibration sensing device comprising:

2. the optical transmission medium includes a first optical transmission path and a second optical transmission path; The forward Mach-Zehnder interferometer comprises: At one end of the optical transmission medium, a forward measurement light source that emits light; a first optical mode coupler that leaves a portion of the fundamental mode light from the forward direction measurement light source as it is in the fundamental mode and converts the remainder into a higher order mode, combines the light that remains in the fundamental mode with the converted light in the higher order mode, and inputs the combined light into the first optical transmission line; At the other end of the optical transmission medium, a second optical mode coupler that, among the light propagating through the first optical transmission line, leaves light in a fundamental mode as it is and converts light in a higher order mode to the fundamental mode, and couples the light that remains in the fundamental mode with the converted light in the fundamental mode; a forward direction measurement optical receiver that receives light from the second optical mode coupler; The reverse Mach-Zehnder interferometer comprises: At the other end of the optical transmission medium, a light source for backward measurement that emits light; a third optical mode coupler that leaves a part of the fundamental mode light from the backward direction measurement light source as the fundamental mode and converts the remainder into a higher order mode, combines the light that remains in the fundamental mode with the converted light in the higher order mode, and inputs the combined light into the second optical transmission line; At one end of the optical transmission medium, a fourth optical mode coupler that, among the light propagating through the second optical transmission line, leaves light in a fundamental mode as it is and converts light in a higher order mode to the fundamental mode, and couples the light that remains in the fundamental mode with the converted light in the fundamental mode; a reverse direction measurement optical receiver that receives light from the fourth optical mode coupler.

2. The optical fiber vibration sensing device according to claim 1,

3. the optical transmission medium includes a first optical transmission path, a second optical transmission path, a third optical transmission path, and a fourth optical transmission path; The forward Mach-Zehnder interferometer comprises: At one end of the optical transmission medium, a forward measurement light source that emits light; a first optical mode coupler that leaves a part of the fundamental mode light from the forward direction measurement light source as it is in the fundamental mode and converts the remainder into a higher order mode, combines the light that remains in the fundamental mode with the converted light in the higher order mode, and inputs the combined light into the first optical transmission line; a forward direction measurement optical receiver that receives light from the third optical transmission path, At the other end of the optical transmission medium, a second optical mode coupler which, among the light propagating through the first optical transmission line, leaves light in a fundamental mode as it is and converts light in a higher-order mode to a fundamental mode, combines the light which remains in the fundamental mode with the converted light in the fundamental mode, and outputs the combined light to the third optical transmission line; The reverse Mach-Zehnder interferometer comprises: At one end of the optical transmission medium, a light source for backward measurement that transmits light to the fourth optical transmission line; a fourth optical mode coupler that, among the light propagating through the second optical transmission line, leaves light in a fundamental mode as it is and converts light in a higher order mode to the fundamental mode, and couples the light that remains in the fundamental mode with the converted light in the fundamental mode; a backward direction measurement optical receiver that receives light from the fourth optical mode coupler, At the other end of the optical transmission medium, a third optical mode coupler that leaves a part of the fundamental mode light from the fourth optical transmission line as the fundamental mode and converts the remainder into a higher-order mode, combines the light that remains in the fundamental mode with the converted light in the higher-order mode, and inputs the combined light into the second optical transmission line; 2. The optical fiber vibration sensing device according to claim 1,

4. The first optical mode coupler or the third optical mode coupler is an off-axis connection part in which the centers of the cores of two optical fibers are connected with a deviation from each other.

4. The optical fiber vibration sensing device according to claim 2 or 3.

5. An optical fiber on the side of the forward measurement light source of the axially offset connection portion as the first optical mode coupler or on the side of the backward measurement light source of the axially offset connection portion as the third optical mode coupler propagates only light of a fundamental mode.

5. The optical fiber vibration sensing device according to claim 4.

6. The second optical mode coupler or the fourth optical mode coupler is an off-axis connection section in which the centers of the cores of two optical fibers are connected with a deviation, and an optical fiber on the side of the forward direction measurement receiver of the off-axis connection section as the second optical mode coupler or on the side of the reverse direction measurement receiver of the off-axis connection section as the fourth optical mode coupler propagates only light of a fundamental mode.

6. The optical fiber vibration sensing device according to claim 2, wherein the optical fiber vibration sensing device is a vibration sensing device having a first end and a second end.

7. the optical transmission medium comprises an optical transmission path, the forward Mach-Zehnder interferometer and the backward Mach-Zehnder interferometer share a fifth optical mode coupler that combines and branches light at one end of the optical transmission medium, and share a sixth optical mode coupler that combines and branches light at the other end of the optical transmission medium; The forward Mach-Zehnder interferometer comprises: At one end of the optical transmission medium, A forward measurement light source is provided to emit light, the fifth optical mode coupler keeps a part of the fundamental mode light from the forward direction measurement light source as the fundamental mode and converts the remainder into a higher order mode, combines the light kept in the fundamental mode with the converted higher order mode light, and inputs the combined light into the optical transmission line; At the other end of the optical transmission medium, a forward direction measurement receiver for receiving light; the sixth optical mode coupler, among the light propagating through the optical transmission line, leaves the light in a fundamental mode as it is, converts the light in a higher order mode to the fundamental mode, combines the light that remains in the fundamental mode with the converted light in the fundamental mode, and outputs the combined light to the forward direction measurement optical receiver; The reverse Mach-Zehnder interferometer comprises: At the other end of the optical transmission medium, a backward measurement light source that emits light of a wavelength different from that of the forward measurement light source; the sixth optical mode coupler leaves a part of the fundamental mode light from the backward measurement light source as the fundamental mode and converts the remainder into a higher-order mode, combines the light that remains in the fundamental mode with the converted higher-order mode light, and inputs the combined light into the optical transmission line; At one end of the optical transmission medium, a backward direction measurement optical receiver that receives light from the fifth optical mode coupler, Among the light propagating through the optical transmission line in the fifth optical mode coupler, the light in the fundamental mode is left as the fundamental mode, and the light in the higher order mode is converted to the fundamental mode, and the light that is left as the fundamental mode and the converted light in the fundamental mode are combined, and output to the reverse direction measurement optical receiver.

2. The optical fiber vibration sensing device according to claim 1,

8. the optical transmission medium includes a first optical transmission path, a third optical transmission path, and a fourth optical transmission path; the forward Mach-Zehnder interferometer and the backward Mach-Zehnder interferometer share a fifth optical mode coupler that combines and branches light at one end of the optical transmission medium, and share a sixth optical mode coupler that combines and branches light at the other end of the optical transmission medium; The forward Mach-Zehnder interferometer comprises: At one end of the optical transmission medium, a forward measurement light source that emits light; a forward direction measurement optical receiver that receives light from the third optical transmission path, the fifth optical mode coupler keeps a part of the fundamental mode light from the forward direction measurement light source as the fundamental mode and converts the remainder into a higher order mode, combines the light kept in the fundamental mode with the converted higher order mode light, and inputs the combined light into the first optical transmission path; At the other end of the optical transmission medium, the sixth optical mode coupler, among the light propagating through the first optical transmission line, leaves the light in fundamental mode as it is, converts the light in higher-order modes to fundamental mode, combines the light that remains in the fundamental mode with the converted light in fundamental mode, and outputs the combined light to the third optical transmission line; The reverse Mach-Zehnder interferometer comprises: At one end of the optical transmission medium, a backward direction measurement light source that transmits light of a wavelength different from that of the forward direction measurement light source to the fourth optical transmission line; a backward direction measurement optical receiver that receives light from the fifth optical mode coupler, the fifth optical mode coupler, among the light propagating through the first optical transmission line, leaves the light in a fundamental mode as it is, converts the light in a higher order mode to a fundamental mode, combines the light that remains in the fundamental mode with the converted light in the fundamental mode, and outputs the combined light to the backward direction measurement light source; At the other end of the optical transmission medium, The sixth optical mode coupler keeps a part of the fundamental mode light from the fourth optical transmission line as the fundamental mode and converts the remainder into a higher-order mode, combines the light kept in the fundamental mode with the converted higher-order mode light, and inputs the combined light into the first optical transmission line.

2. The optical fiber vibration sensing device according to claim 1,

9. a first AD converter that performs AD conversion on an electrical signal from the forward Mach-Zehnder interferometer; a second AD converter that AD converts an electrical signal from the reverse Mach-Zehnder interferometer; an analysis device that identifies a location where vibration occurs using a signal from the first AD converter and a signal from the second AD converter; 2. The optical fiber vibration sensing device according to claim 1, further comprising:

10. a first AD converter that performs AD conversion on an electrical signal from the forward direction measurement light receiver; a second AD converter that performs AD conversion on the electrical signal from the reverse direction measurement light receiver; an analysis device that identifies a location where vibration occurs using a signal from the first AD converter and a signal from the second AD converter; 9. The optical fiber vibration sensing device according to claim 2, further comprising:

11. a fixed-time data acquisition step of acquiring interference wave signals w1(t) and w2(t) from a forward Mach-Zehnder interferometer and a backward Mach-Zehnder interferometer in which the light travels in the opposite direction to that of the forward Mach-Zehnder interferometer, respectively; a cross-correlation calculation step of changing τ in formula (8) and determining τ when the correlation value (w1 * w2) (τ) is maximized as ΔT; (w1*w2)(τ) = Σ w1(t)×w2(τ-t) (8) a vibration generation position calculation step of calculating a distance Lv from the other end of the optical transmission line to a point where vibration is applied using equation (4); Lv = (L-c2×ΔT)c1 / (c1+c2) (4) where L is the total length of the optical transmission medium having multiple optical transmission paths. c1 is the speed of light in the optical transmission line of the forward Mach-Zehnder interferometer c2 is the speed of light in the optical transmission line of the reverse Mach-Zehnder interferometer An optical fiber vibration sensing method comprising:

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