Crosstalk measurement device and crosstalk measurement method

Abstract

A crosstalk measurement device (1) is characterized by comprising: a first optical switch (61) capable of selectively switching to any one of a plurality of optical waveguides; a connection optical waveguide for optically connecting the other end (18) of one optical waveguide and the other end (18) of another one optical waveguide among the plurality of optical waveguides; an OTDR (20) that is optically connected to one end of the one optical waveguide via the first optical switch (61), causes light to enter the one optical waveguide from one end (17) thereof as incoming light, and measures the power of light emitted from the one end of the one optical waveguide, the emitted light including crosstalk light (CL1) generated through crosstalk of the incoming light between the one optical waveguide and the other one optical waveguide; and a processing unit (25) for determining crosstalk between the one optical waveguide and the other one optical waveguide by using the measured power of the emitted light.

Description

Crosstalk measuring device and crosstalk measuring method

[0001] The present invention relates to a crosstalk measurement device and a crosstalk measurement method.

[0002] The recent increase in the volume of information and communications traffic has led to a demand for an expansion of the transmission capacity of optical fibers. Multicore fibers have attracted attention because they can improve spatial utilization efficiency and transmit large amounts of information in a limited space. However, because multiple cores are arranged in a single optical fiber, evaluating their characteristics is more difficult than with single-core fibers. Therefore, there is a demand for technology to efficiently evaluate multicore fibers. In particular, crosstalk measurement is an important measurement item for multicore fibers, but is not available for single-core fibers, so new measurement equipment must be prepared.

[0003] The methods described in the following non-patent documents are known as crosstalk measurement methods. Non-patent document 1 below describes a PM (Power Meter) method. The PM method is a method in which light is incident on one end of a predetermined core of a multi-core fiber, and the power of light emitted from the other end of a core that crosstalks with the incident core is measured. Non-patent documents 2 and 3 below describe an OTDR (Optical Time Domain Reflectometer) method. In the OTDR method, a multi-channel OTDR is used to incident light on a predetermined core, and light that crosstalks with other cores due to backscattered light of the incident light is detected, thereby measuring crosstalk.

[0004] In the crosstalk measurement methods described in Non-Patent Documents 2 and 3, the power of the light to be measured is small because backscattered light of light after crosstalk is measured, which raises concerns that it may be difficult to measure crosstalk. In a multi-core fiber with small crosstalk, measuring crosstalk is even more difficult.

[0005] On the other hand, the PM method requires that light be incident on one end of a multi-core fiber and that light exiting from the other end be received. The OTDR method requires that light be incident on one end of a multi-core fiber and that light exiting from the one end be received. For this reason, there is a need to measure crosstalk using an OTDR.

[0006] In response to the above needs, the crosstalk measurement method described in Non-Patent Document 4 optically connects a predetermined core and another core, whose crosstalk between the predetermined core and the predetermined core is to be measured, via an optical fiber at the other end of a multicore fiber, and measures the power of crosstalk light generated by the crosstalk using an OTDR. In this crosstalk measurement method, the OTDR makes incident light incident on one end of the predetermined core, and this incident light generates crosstalk light in another core optically connected to the optical fiber, and light including the crosstalk light that entered the predetermined core from the other core via the optical fiber is output from one end of the predetermined core. The power of this output light is measured by the OTDR. Furthermore, this crosstalk measurement method determines the crosstalk between the predetermined core and the other cores based on the power of the measured light.

[0007] K. Takenaga, Y. Arakawa, S. Tanigawa, N. Guan, S. Matsuo, K. Saitoh and M. Koshiba, “An Investigation on Crosstalk in Multi-Core Fibers by Introducing Random Fluctuation along Longitudinal Direction,” IEICE TRAN. COMMUN., Vol.E94-B, No.2, 2011.M. Ohashi, K. Kawazu, A. Nakamura, and Y. Miyoshi,“Simple backscattered power technique for measuring crosstalk of mul1ti-core fibers,” OptoElectronics and Communications Conference, Busan, South Korea, P1-25, 2012, DOI: https: / / doi.org / 10.1109 / OECC.2012.6276724M. Nakazawa, M. Yoshida, and T. Hirooka, “Nondestructive measurement of mode couplings along a multi-core fiber using a synchronous multi-channel OTDR,” Optics Express, vol. 20, Issue 11, pp. 12530-12540, 2012M. Nakagawa, M. Ohzeki, K. Takenaga and K. Ichii, “Novel Inter-Core Crosstalk Measurement Method Using a Loopback and Bidirectional OTDR Technique,” Journal of Lightwave Technology, vol. 41, Issue 12, pp. 3842-3848, 2023

[0008] Incidentally, in such a crosstalk measurement method, the OTDR can be optically reconnected to one end of the other core and incident light can be made incident on one end of the other core, thereby generating crosstalk light from the other core to a specified core, and the crosstalk between the other core and the specified core can be determined.

[0009] Furthermore, when the multicore fiber has three or more cores, the above-mentioned crosstalk measurement method requires optically reconnecting the other end of the specified core to the other end of another core different from the other core, thereby switching from a state in which crosstalk between the specified core and the other core is measured to a state in which crosstalk between the specified core and the other core is measured.

[0010] Therefore, there is a demand for the above-mentioned crosstalk measurement method to measure crosstalk by easily switching the optical connection between the OTDR and the cores or by easily switching the optical connection of the cores at the other end of the multicore fiber. That is, there is a demand for the above-mentioned crosstalk measurement method to measure crosstalk by easily switching the optical path.

[0011] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a crosstalk measuring device and a crosstalk measuring method that can easily switch optical paths and measure crosstalk using an OTDR.

[0012] In order to solve the above-described problems, a first aspect of the present invention is a crosstalk measurement apparatus for an optical device having a plurality of optical waveguides arranged in parallel with one another, each including one end and the other end, the crosstalk measurement apparatus comprising: a first optical switch capable of selectively switching one of the plurality of optical waveguides; a connecting optical waveguide that optically connects the other end of the one optical waveguide to the other end of another of the plurality of optical waveguides; an OTDR that is optically connected to one end of the one optical waveguide via the first optical switch, and that receives incident light from the one end of the one optical waveguide and measures the power of output light that includes crosstalk light generated when the incident light crosstalks between the one optical waveguide and the other optical waveguide; and a processing unit that calculates the crosstalk between the one optical waveguide and the other optical waveguide using the measured power of the output light.

[0013] The crosstalk measurement device of this embodiment can selectively switch the optical connection between the OTDR and one end of one of the optical waveguides via the first optical switch. Therefore, the crosstalk measurement device of this embodiment can easily switch the optical waveguide to which incident light is incident from the OTDR. Therefore, the crosstalk measurement device of this embodiment can easily switch the optical path using the OTDR to measure crosstalk. Note that in a pair of optical waveguides whose other ends are optically connected to each other via a connecting optical waveguide, the propagation directions of light are opposite and the optical paths are different between a measurement in which light is incident from one end of one optical waveguide to measure crosstalk between the one optical waveguide and the other optical waveguide and a measurement in which light is incident from one end of the other optical waveguide to measure crosstalk between the other optical waveguide and the one optical waveguide.

[0014] A second aspect of the present invention is the crosstalk measuring device according to the first aspect, characterized in that the plurality of optical waveguides are three or more optical waveguides, and a second optical switch is connected to the connecting optical waveguide, the second optical switch being capable of selectively switching any one of the plurality of optical waveguides other than the one optical waveguide as the other one optical waveguide.

[0015] The crosstalk measurement device of this embodiment can further selectively switch the optical connection between the other end of the optical waveguide optically connected to the OTDR and the other end of any other optical waveguide via the second optical switch, thereby easily switching the optical connection between the optical waveguide optically connected to the OTDR and another optical waveguide.

[0016] A third aspect of the present invention is the crosstalk measuring device according to the second aspect, characterized in that, when the selection of the one optical waveguide is switched by the first optical switch, the second optical switch is capable of switching from an optical connection between the one optical waveguide and the other one optical waveguide before switching to an optical connection between the one optical waveguide and the other one optical waveguide after switching.

[0017] Even when the optical waveguide optically connected to the OTDR is switched, the crosstalk measurement device of this embodiment can optically connect the optical waveguide optically connected to the OTDR at its other end to any other optical waveguide, and therefore the crosstalk measurement device of this embodiment can easily change the combination of optical waveguides for which crosstalk is measured.

[0018] A fourth aspect of the present invention is a crosstalk measurement apparatus for an optical device having three or more optical waveguides arranged in parallel, each including one end and the other end, the crosstalk measurement apparatus comprising: a second optical switch capable of selectively switching any of the optical waveguides other than one of the plurality of optical waveguides, the connecting optical waveguide optically connecting the other end of the one optical waveguide to the other end of another optical waveguide; an OTDR optically connected to one end of the one optical waveguide, which receives incident light from the one end of the one optical waveguide and measures the power of output light output from the one end of the one optical waveguide, the output light including crosstalk light generated when the incident light crosstalks between the one optical waveguide and the other optical waveguide; and a processing unit which calculates the crosstalk between the one optical waveguide and the other optical waveguide using the measured power of the output light.

[0019] The crosstalk measurement device of this embodiment can selectively switch the optical connection between the other end of the optical waveguide optically connected to the OTDR and the other end of any other optical waveguide via the second optical switch. Therefore, the crosstalk measurement device of this embodiment can easily switch the optical connection between the optical waveguide optically connected to the OTDR and another optical waveguide. Therefore, the crosstalk measurement device of this embodiment can easily switch the optical path using the OTDR and measure crosstalk.

[0020] A fifth aspect of the present invention is a method for measuring crosstalk in an optical device having a plurality of optical waveguides arranged in parallel with one another, each having one end and the other end, the method comprising: a first connecting step of optically connecting an OTDR and one end of one of the optical waveguides via a first optical switch capable of selectively switching any one of the plurality of optical waveguides; a second connecting step of optically connecting the other end of the one optical waveguide to the other end of another of the plurality of optical waveguides via a connecting optical waveguide; a measuring step of making outgoing incident light incident from the one end of the one optical waveguide, the incident light including crosstalk light generated by crosstalk between the one optical waveguide and the other one optical waveguide, and measuring the power of outgoing light outgoing from the one end of the one optical waveguide with the OTDR; and a processing step of determining the crosstalk between the one optical waveguide and the other one optical waveguide using the measured power of the outgoing light.

[0021] The crosstalk measurement method of this embodiment can selectively switch the optical connection between the OTDR and one end of any one of the optical waveguides via the first optical switch. Therefore, the crosstalk measurement method of this embodiment can easily switch the optical waveguide onto which incident light is incident from the OTDR. Therefore, the crosstalk measurement method of this embodiment can easily switch the optical path using the OTDR and measure crosstalk.

[0022] A sixth aspect of the present invention is a method for measuring crosstalk in an optical device having three or more optical waveguides arranged in parallel, each including one end and the other end, the method including: a first connecting step of optically connecting an OTDR to one end of one of the plurality of optical waveguides; and a second optical switch of optically connecting, via a connecting optical waveguide including a second optical switch capable of selectively switching any one of the plurality of optical waveguides other than the one optical waveguide, the other end of the one optical waveguide to the other end of another one of the optical waveguides selected by the second optical switch. a connecting step; a measuring step of making incident light output from the OTDR incident on the one end of the one optical waveguide and measuring, with the OTDR, the power of output light that includes crosstalk light generated by crosstalk between the one optical waveguide and the other optical waveguide and that is output from the one end of the one optical waveguide; and a processing step of determining the crosstalk between the one optical waveguide and the other optical waveguide using the measured power of the output light.

[0023] The crosstalk measurement method of this embodiment can selectively switch the optical connection between the other end of the optical waveguide optically connected to the OTDR and the other end of any other optical waveguide via the second optical switch. Therefore, the crosstalk measurement method of this embodiment can easily switch the optical connection between the optical waveguide optically connected to the OTDR and another optical waveguide. Therefore, the crosstalk measurement method of this embodiment can easily switch the optical path using the OTDR and measure crosstalk.

[0024] As described above, the present invention provides a crosstalk measurement device and a crosstalk measurement method that use an OTDR to easily switch optical paths and measure crosstalk.

[0025] Fig. 5 is a diagram showing a cross section perpendicular to the longitudinal direction of a multi-core fiber according to a first embodiment of the present invention. Fig. 6 is a diagram showing a crosstalk measurement device in the first embodiment. Fig. 7 is a flowchart showing the procedure of a crosstalk measurement method in the first embodiment of the present invention. Fig. 8 is a diagram showing the state of light propagation in the crosstalk measurement device of Fig. 2. Fig. 9 is a diagram showing measurement results by an OTDR. Fig. 10 is an enlarged view of a part of Fig. 5. Fig. 11 is a diagram showing a crosstalk measurement device in a second embodiment.

[0026] Below, embodiments for carrying out the crosstalk measurement method and crosstalk measurement device according to the present invention are illustrated with reference to the accompanying drawings. The embodiments illustrated below are intended to facilitate understanding of the present invention and are not intended to limit the present invention. The present invention can be modified and improved from the following embodiments without departing from the spirit and scope of the claims. Note that in the drawings referred to below, the dimensions of each component may be changed to facilitate understanding.

[0027] 1 is a diagram showing a cross section perpendicular to the longitudinal direction of a multicore fiber of this embodiment. A multicore fiber 10 has a plurality of cores 11 to 14 through which light can propagate, and a cladding 15 that surrounds the outer peripheral surfaces of each of the cores 11 to 14. The outer peripheral surface of the cladding 15 may be surrounded by a coating layer made of resin.

[0028] Each of the cores 11 to 14 has one end and the other end, and is arranged in parallel with one another along the longitudinal direction of the multicore fiber 10. The refractive index of the cores 11 to 14 is higher than the refractive index of the cladding 15, and light can propagate through each of the cores 11 to 14. Therefore, each of the cores 11 to 14 is an optical waveguide, and the multicore fiber 10 is an optical device having a plurality of optical waveguides arranged in parallel with one another.

[0029] In this embodiment, the cores 11 to 14 are made of silica glass doped with a dopant that increases the refractive index, such as germanium (Ge), and the clad 15 is made of silica glass with no doping. Note that, for example, the cores 11 to 14 may be made of silica glass with no doping and the clad 15 may be made of silica glass doped with a dopant that decreases the refractive index, such as fluorine (F), or the cores 11 to 14 may be made of silica glass doped with a dopant that increases the refractive index and the clad 15 may be made of silica glass doped with a dopant that decreases the refractive index. Furthermore, the dopants that increase the refractive index and the dopants that decrease the refractive index are not particularly limited.

[0030] Next, a crosstalk measurement device for an optical device according to this embodiment will be described. Fig. 2 is a diagram showing the crosstalk measurement device according to this embodiment. As shown in Fig. 2, the crosstalk measurement device 1 according to this embodiment mainly comprises an OTDR 20, a processing unit 25, a connecting optical waveguide member 51, and a first optical switch 61, and measures crosstalk in a multicore fiber 10. The multicore fiber 10 has one end 17 and the other end 18. In the following description, the one end 17 and the other end 18 may also be referred to as the one ends 17 and the other ends 18 of the cores 11 to 14.

[0031] The OTDR 20 is used by being connected to an optical fiber or the like, and is an instrument that emits pulsed light, measures the power of light incident from the multicore fiber 10, and measures the time from when the pulsed light is emitted until the measured light is incident, and is capable of measuring light losses such as transmission loss, bending loss, connection loss, etc. of optical fibers, etc., detecting broken portions of optical fibers, etc., measuring the amount of light reflection, etc. In this embodiment, a first optical switch 61 is optically connected to the OTDR 20 via an optical fiber.

[0032] The first optical switch 61 has one end and a plurality of other ends. The first optical switch 61 switches an internal waveguide to selectively switch the optical connection between the one end and one of the other ends. The first optical switch 61 may switch the optical connection between the one end and one of the other ends based on a control signal from a control unit (not shown), or may switch the optical connection between the one end and one of the other ends by user operation.

[0033] One end of the first optical switch 61 is optically connected to the OTDR 20. The other end of the first optical switch 61 is connected to each of the optical fibers 31 to 34 of the fan-in-fan-out device 30. Therefore, the first optical switch 61 can selectively optically connect the OTDR 20 to any of the cores of the optical fibers 31 to 34 and switch the connection.

[0034] The fan-in-fan-out device 30 has a plurality of optical waveguides (not shown) that can be optically connected individually to the cores 11 to 14 at one end 17 of the multicore fiber 10, and optical fibers 31 to 34 that include cores that are optically connected individually to the respective optical waveguides. In this example, the one ends 17 of the cores 11 to 14 are optically connected to the cores of the optical fibers 31 to 34, respectively. Therefore, in this embodiment, the first optical switch 61 can selectively switch the optical connection between the OTDR 20 and any one of the cores 11 to 14 via the fan-in-fan-out device 30.

[0035] A fan-in-fan-out device 40 is connected to the other end 18 of the multicore fiber 10. The fan-in-fan-out device 40 has a configuration similar to that of the fan-in-fan-out device 30, and the cores of optical fibers 41 to 44 are individually optically connected to a plurality of optical waveguides (not shown) that are individually optically connectable to the cores 11 to 14 of the multicore fiber 10. In this example, the other ends 18 of the cores 11 to 14 and the cores of the optical fibers 41 to 44 are optically connected, respectively.

[0036] The connecting optical waveguide member 51 includes connecting optical fibers 51a to 51d and a second optical switch 62. The connecting optical fibers 51a to 51d are single-core fibers, such as single-mode fibers. One end of the connecting optical fibers 51a to 51d is connected to the optical fibers 41 to 44, respectively.

[0037] The second optical switch 62 has one end and a plurality of other ends. The second optical switch 62 switches an internal waveguide to selectively switch the optical connection between the one end and one of the other ends. The second optical switch 62 may switch the optical connection between the one end and one of the other ends based on a control signal from a control unit (not shown), or may switch the optical connection between the one end and one of the other ends by user operation.

[0038] One end of the second optical switch 62 is connected to the other end of the connecting optical fiber 51a. The other end of the second optical switch 62 is connected to the other ends of the connecting optical fibers 51b to 51d, respectively. Therefore, the second optical switch 62 can selectively switch the optical connection between the core of the optical fiber 41 and any of the cores of the optical fibers 42 to 44. In other words, the second optical switch 62 can selectively switch the optical connection between the core 11 and any of the cores 12 to 14.

[0039] In the connecting optical waveguide member 51, the core of the connecting optical fiber 51a and the cores of the connecting optical fibers 51b to 51d are connecting waveguides that optically connect the other end of the core 11 to the other end of any one of the cores 12 to 14, and a second optical switch 62 is connected to the connecting waveguides. The second optical switch 62 is preferably provided at a point other than the midpoint of the optical path from the other end 18 of the core 11 to the other end 18 of each of the cores 12 to 14. For this reason, for example, the length of the connecting optical fiber 51a is 1 km, and the length of the connecting optical fibers 51b to 51d is 10 km.

[0040] A processing unit 25 is connected to the OTDR 20, and data related to the power of light received by the OTDR 20 is output to the processing unit 25. The processing unit 25 is a calculation device that calculates crosstalk using the power of light measured by the OTDR 20. The processing unit 25 can be, for example, an integrated circuit such as a microcontroller, an integrated circuit (IC), a large-scale integrated circuit (LSI), or an application-specific integrated circuit (ASIC), or an NC (numerical control) device. Furthermore, when an NC device is used as the processing unit 25, the processing unit 25 may or may not use a machine learning device. When the data related to the power of light is input from the OTDR 20, the processing unit 25 calculates the crosstalk between the core 11 and any one of the cores 12 to 14 based on this data, as described below, and outputs data related to the calculated crosstalk. The processing unit 25 and the OTDR 20 may be housed in a single housing, and some components may be shared. It should be noted that the components constituting the processing section 25 may also serve as a control section (not shown) that controls the switching of the first optical switch 61 and the second optical switch 62 described above.

[0041] Next, a crosstalk measurement method for an optical device according to this embodiment will be described. Fig. 3 is a flowchart showing the steps of the crosstalk measurement method according to this embodiment. As shown in Fig. 3, the crosstalk measurement method according to this embodiment includes a first connection step S1, a second connection step, a measurement step S3, and a processing step S4.

[0042] (First Connection Step S1) Prior to this step, a multi-core fiber 10 is prepared as an optical device to be measured and set in the crosstalk measurement apparatus 1. The length of the multi-core fiber 10 is, for example, 21 km.

[0043] This step optically connects the OTDR 20 to one end 17 of any one of the cores 11 to 14 via the first optical switch 61. In this step, the OTDR 20 is optically connected to any one of the cores 11 to 14 via the first optical switch 61. Specifically, the OTDR 20 is optically connected to any one of the optical fibers 31 to 34 in the fan-in-fan-out device 30 using the first optical switch 61. In this example, the first optical switch 61 is operated so that one end of the first optical switch 61 is optically connected to the other end connected to the optical fiber 31. Therefore, the OTDR 20 and the core of the optical fiber 31 are optically connected via the first optical switch 61. Therefore, the OTDR 20 and the core 11 are optically connected.

[0044] (Second Connection Step S2) This step optically connects the other end 18 of one core to the other end 18 of another one of the cores 12 to 14 via a connecting optical waveguide. In this step, the other end 18 of the core 11 is optically connected to the other end 18 of any one of the cores 12 to 14 via the second optical switch 62. Specifically, the second optical switch 62 is used to optically connect the core of the optical fiber 41 in the fan-in-fan-out device 40 to one of the cores of the optical fibers 42 to 44. Therefore, in this step, the other end of the core 11, to which the OTDR 20 is optically connected, is optically connected to the other end of any one of the cores 12 to 14 via the second optical switch 62. Therefore, the second optical switch 62 can selectively switch any one of the multiple optical waveguides other than the one optical waveguide optically connected to the OTDR 20.

[0045] In this example, the second optical switch 62 is operated so that one end of the second optical switch 62 is optically connected to the other end connected to the connecting optical fiber 51 b. Therefore, the core of the connecting optical fiber 51 a and the core of the connecting optical fiber 51 b are optically connected via the second optical switch 62. Therefore, the other end 18 of the core 11 and the other end 18 of the core 12 are optically connected via the second optical switch 62.

[0046] After this step, when light is incident from one end 17 of the core 11, the light passes through the cores of the connecting optical fibers 51a and 51b and enters the core 12 from the other end 18 of the core 12.

[0047] (Measurement Step S3) This step is a step in which incident light output from the OTDR 20 is made incident from one end 17 of one core, and the power of output light including crosstalk light generated by crosstalk between the incident light and the one core and output from one end 17 of one core is measured by the OTDR 20. As described above, the OTDR 20 is optically connected to one end 17 of the core 11 via the first optical switch 61, and the other end 18 of the core 11 is optically connected to the other end 18 of the core 12 via the second optical switch 62. Therefore, in this step, the pulsed incident light output from the OTDR 20 is input from one end 17 of the core 11, and the power of the output light output from one end 17 of the core 11 is measured by the OTDR 20, which includes pulsed light that is a combination of light generated by the incident light crosstalking from core 11 to core 12 and light generated by the incident light entering from core 11 to core 12 via the connecting optical waveguide member 51 crosstalking from core 12 to core 11.

[0048] FIG. 4 is a diagram showing the propagation of light in the crosstalk measurement device of FIG. 2. The above will be explained in detail using this diagram. Note that the fan-in-fan-out devices 30 and 40 are depicted in a simplified manner in FIG. 4. The connecting optical fibers 51c and 51d are also omitted. First, pulsed light is emitted from the OTDR 20. The wavelength width of this light is preferably 1 nm or more from the viewpoint of stable crosstalk measurement (described later), more preferably 3 nm or more, and even more preferably 5 nm or more. Furthermore, the wavelength width of this light is preferably 30 nm or less from the viewpoint of measuring crosstalk at a specific wavelength. Furthermore, it is preferable that the power of the light emitted from the OTDR 20 be adjusted appropriately to prevent saturation of the emitted light, including the crosstalk light (described later). In this case, an attenuator may be interposed between the OTDR 20 and the optical fiber 31.

[0049] Pulsed light emitted from the OTDR 20 enters the core 11 from one end 17 of the core 11 as incident light and propagates through the core 11 from the one end 17 to the other end 18. The pulsed incident light propagating through the core 11 propagates from the core 11 to the core 12 while causing crosstalk. Because the incident light L is pulsed, crosstalk light CL1 that crosstalks from the core 11 to the core 12 also becomes pulsed and propagates from the one end 17 to the other end 18 of the core 12 while traveling generally parallel to the incident light L. During this time, because crosstalk occurs from the core 11 to the core 12, the power of the incident light L decreases depending on the distance it propagates through the core 11, and the power of the crosstalk light CL1 increases depending on the distance it propagates through the core 12. Because the speed of light propagating through the core 11 and the core 12 is the same, the incident light L and the crosstalk light CL1 reach the other end 18 generally at the same time.

[0050] Next, the incident light L and the crosstalk light CL1 are incident on the cores of the connecting optical fiber 51a and the connecting optical fiber 51b at approximately the same time, respectively, via the fan-in-fan-out device 40. The incident light L incident on the core of the connecting optical fiber 51a and the crosstalk light CL1 incident on the core of the connecting optical fiber 51b intersect at approximately the midpoint of the optical path between the other end 18 of the core 11 and the other end 18 of the core 12, i.e., the connecting optical waveguide. The incident light L reaches the end of the connecting optical fiber 51b, and at approximately the same time, the crosstalk light CL1 reaches the end of the connecting optical fiber 51a. Then, via the fan-in-fan-out device 40, the incident light L is incident on the core 12 from the other end 18 of the core 12, and the crosstalk light CL1 is incident on the core 11 from the other end 18 of the core 11. At this time, the incident light L and the crosstalk light CL1 are incident on the cores 12 and 11 at approximately the same time. Even if the lengths of the optical fiber 41 and the optical fiber 42 in the fan-in-fan-out device 40 are different, the incident light L and the crosstalk light CL1 are incident on the cores 12 and 11 at approximately the same time.

[0051] The incident light L incident on the core 12 and the crosstalk light CL1 incident on the core 11 propagate through the respective cores 12 and 11 toward one end 17 while traveling roughly parallel to one another. During this time, the incident light L propagating through the core 12 also propagates through the core 11 while causing crosstalk to the core 11. Therefore, the light that crosstalks from the core 12 to the core 11 is combined with the crosstalk light CL1 propagating through the core 11. The combined light is pulsed and propagates while gradually increasing in power. Outgoing light, which is the pulsed crosstalk light CL1 combined with light such as backscattered light, is emitted from one end 17 of the core 11. Therefore, the outgoing light includes the pulsed crosstalk light CL1.

[0052] The light emitted from the core 11 is incident on the OTDR 20 via the fan-in-fan-out device 30, and is received by the OTDR 20, where its power is measured.

[0053] FIG. 5 is a diagram showing the measurement results of the output light received by the OTDR 20. In FIG. 5, the horizontal axis represents the propagation distance of the incident light L, and the vertical axis represents the power of the output light received by the OTDR 20. The vertical axis of FIG. 5 represents the power of the output light in decibels as a ratio to a predetermined power set for the OTDR 20. For example, if this predetermined power is 1 mW, the vertical axis may be expressed in dBm. In addition, in the measurement to obtain FIG. 5, in order to reproduce a state in which the second optical switch 62 optically connects the cores 11 and 12, the cores 11 and 12 were connected by an optical fiber as a connecting optical waveguide member. As shown in FIG. 5, backscattered light was measured as the output light in the section where the incident light L propagates through the core 11 and the section where the incident light L propagates through the core 12. The slope of the line representing the output light in these sections indicates the loss of the incident light L per unit length due to backscattering. Furthermore, pulsed light is measured at the boundary between the section of the core 11 and the section of the connecting optical waveguide member 51, and at the boundary between the section of the connecting optical waveguide member 51 and the section of the core 12, and this light indicates reflection in the fan-in-fan-out device 40, etc. Furthermore, pulsed light is measured on the core 11 side of the midpoint of the connecting optical waveguide member 51, and this light indicates reflection in the second optical switch 62.

[0054] Pulsed light is measured approximately at the midpoint of the optical path between the other end 18 of core 11 and the other end 18 of core 12. As described above, the incident light L and the crosstalk light CL1 intersect approximately at the midpoint of the optical path, and therefore this pulsed light represents the crosstalk light CL1. Furthermore, backscattered light is measured as emitted light in the section where the incident light L propagates through the connecting optical waveguide member 51. Therefore, the power of the emitted light measured approximately at the midpoint of the optical path includes the power of the crosstalk light CL1 and the power of the backscattered light.

[0055] As described above, a pulse indicating the power of the crosstalk light CL1 is shown at approximately the midpoint of the optical path. The pulse width of the incident light L and the pulse width of the crosstalk light CL1 are approximately the same. Therefore, in order to prevent the pulse indicating the crosstalk light CL1 from reaching the end of the connecting optical waveguide member 51, it is preferable that the optical path length of the connecting optical waveguide member 51 is longer than the half-width of the incident light L. In other words, if the total length is L SCF and the half-value time width of the incident light L is ΔT pulse When the refractive index of each core of the connecting optical fibers 51a and 51b is n and the high speed is c, it is preferable to satisfy the following formula: SCF >ΔT pulse ×c / n

[0056] It is more preferable to satisfy the following formula in order to further suppress the influence of the end of the connecting optical waveguide member 51 on the pulse: L SCF >1.2 x ΔT pulse ×c / n

[0057] The OTDR 20 outputs data relating to the measured power of the emitted light to the processing unit 25 .

[0058] (Processing Step S4) This step is a step of determining the crosstalk between one core and another core using the power of the measured emitted light. In this step, the crosstalk between core 11 and core 12 is determined using the power of the measured emitted light. FIG. 6 is an enlarged view of the emitted light measured approximately at the midpoint in FIG. 5. As described above, backscattered light is also generated in the connecting optical waveguide member 51. Therefore, the power of this backscattered light is measured in areas other than the area where pulsed light is displayed. Therefore, based on the data input from the OTDR 20, the processing unit 25 first calculates the power P of the backscattered light in the area where pulsed light is displayed from the power of the emitted light in areas other than the area where pulsed light including the crosstalk light CL1 is displayed. BS Specifically, the processing unit 25 linearly approximates the power of the emitted light in the region other than the region where the pulsed light is displayed, and calculates the power P of the backscattered light. BS Next, the processing unit 25 calculates the power P of the emitted light in the region where the pulsed light is shown. OUT The power of the backscattered light P BS This difference is the power of the pulsed light. However, the power of this pulsed light includes the power P of the crosstalk light CL1. XT_MCF and the crosstalk power P XT_FIFO It includes Power P XT_FIFO When the power of the pulsed light is negligibly small, the power of the crosstalk light CL1 is XT－MCF However, the power P XT_FIFO The power after removing the crosstalk light CL1 is the power P XT_MCF This will give a more accurate power P XT_MCF Furthermore, taking the insertion loss of the second optical switch 62 into consideration is preferable from the viewpoint of obtaining the power P XT_MCF This is preferable from the viewpoint of obtaining the above.

[0059] Power P XT_FIFOcan be measured in advance. For example, in the crosstalk measurement apparatus 1, the fan-in-fan-out device 30 and the fan-in-fan-out device 40 are directly optically connected. By doing so, the length of the multicore fiber 10 becomes 0, and when the power of the emitted light is measured in the same manner as in the measurement step S3 described above, the power P of the pulsed light measured at approximately the midpoint of the optical path formed by each of the optical fibers 41, 42 and the connecting optical waveguide member 51 is OUT Power P XT_FIFO and Power P BS Therefore, in the same manner as above, the power P OUT and Power P BS By calculating the difference between XT_FIFO can be obtained.

[0060] The processing unit 25 calculates the power P of the crosstalk light CL1. XT_MCF The crosstalk is converted into crosstalk and output. At this time, the processing unit 25 may convert the crosstalk into decibels that indicate the ratio of the power of the incident light L emitted from one end 17 of the core 12 and output the converted crosstalk. Alternatively, the processing unit 25 may convert the crosstalk into decibels that indicate the ratio to a predetermined power determined in the OTDR 20 shown in Figures 5 and 6 and output the converted crosstalk. In this way, the crosstalk is determined.

[0061] In the crosstalk measurement method of this embodiment, the first optical switch 61 may switch the selection of cores 11 to 14, and the crosstalk measurement device 1 may measure crosstalk again. For example, the first optical switch 61 may be switched to optically connect the OTDR 20 to one end 17 of core 12. That is, the optical path along which incident light from the OTDR 20 propagates is switched from the order of core 11, core 12 to the order of core 12, core 11. In this state, the OTDR measures the power of light emitted from one end 17 of core 12. The processing unit 25 inverts the range from core 12 to core 11 of the measured light power distribution along the horizontal axis. Then, the processing unit 25 calculates the arithmetic mean of the light power distribution in the range from core 11 to core 12 measured in measurement step S3 and the inverted light power distribution. By doing so, the power of light backscattered as it propagates through the core 11 from one end 17 to the other end 18 and the power of light backscattered as it propagates through the core 11 from the other end 18 to the one end 17 are averaged, and the gradient of the light power distribution within the range of core 11 in FIG. 5 is substantially eliminated. Similarly, the gradient of the light power distribution representing the range of core 12 in FIG. 5 and the gradient of the light power distribution within the range of the connecting optical waveguide member 51 are substantially eliminated. Furthermore, pulsed crosstalk light, which is an average of the crosstalk light CL1 and the crosstalk light measured in that state, appears approximately at the midpoint of the optical path between the other end 18 of core 11 and the other end 18 of core 12. The processing unit 25 calculates the crosstalk from the power of the averaged pulsed crosstalk light.

[0062] Furthermore, in the crosstalk measurement method of this embodiment, the second optical switch 62 may switch the selection of cores 12 to 14, and the crosstalk measurement device 1 may measure crosstalk again. For example, the second optical switch 62 may be switched to optically connect the other end 18 of core 11 to the other end 18 of core 13. That is, the optical path along which the incident light from the OTDR 20 propagates is switched from the order of core 11, core 12 to the order of core 11, core 13. In this state, as described above, the OTDR measures the power of the light emitted from one end 17 of core 11. The processing unit 25 calculates the crosstalk between core 11 and core 13 based on the measured power.

[0063] Furthermore, in the crosstalk measurement method of this embodiment, the crosstalk measurement device 1 may measure crosstalk by switching both the selection of the cores 11 to 14 by the first optical switch 61 and the selection of the cores 12 to 14 by the second optical switch 62. However, the second optical switch 62 is switched so that the other end 18 of the core selected by the first optical switch 61 is optically connected to the other end 18 of a core other than the core selected by the first optical switch 61.

[0064] Furthermore, the crosstalk measurement device 1 may be provided with an optical component in the connecting optical fiber 51a such that the loss of light incident from the core 11 side to the second optical switch 62 side is greater than the loss of light incident from the second optical switch 62 side to the core 11 side. In this case, the optical component is disposed closer to the core 11 than the midpoint of the optical path between the other end of the core 11 and the other end of any of the cores 12 to 14. For example, the optical component may be an isolator, a circulator, or a coupler. The optical component prevents the incident light L from being incident on the midpoint, thereby preventing backscattered light and noise generated from the backscattered light from being superimposed on the crosstalk light CL1. Therefore, the crosstalk measurement device 1 can accurately measure the power of the crosstalk light CL1 and accurately measure crosstalk.

[0065] As described above, in the crosstalk measurement method and crosstalk measurement device 1 of this embodiment, the optical connection between the OTDR 20 and one end of any one of the cores can be selectively switched via the first optical switch 61. Therefore, the crosstalk measurement method and crosstalk measurement device 1 of this embodiment can easily switch the core onto which incident light from the OTDR 20 is incident. Furthermore, the crosstalk measurement method of this embodiment can selectively switch the optical connection between the other end of one core optically connected to the OTDR 20 and the other end of any other core via the second optical switch 62. Therefore, the crosstalk measurement method and crosstalk measurement device 1 of this embodiment can easily switch the optical connection between one core optically connected to the OTDR and another core. Therefore, the crosstalk measurement method of this embodiment can easily switch the optical path and measure crosstalk using the OTDR.

[0066] Second Embodiment Next, a second embodiment will be described. Components that are the same as or equivalent to those in the first embodiment are denoted by the same reference numerals and will not be described again unless otherwise specified. This embodiment differs from the first embodiment in that the other end 18 of core 11 or core 12 is selectively optically connected to the other end 18 of core 13 or core 14 via a second optical switch 62.

[0067] 7 , the second optical switch 62 has a plurality of one ends and a plurality of other ends. In this embodiment, the second optical switch 62 has two one ends and two other ends. The second optical switch 62 switches an internal waveguide to selectively switch the optical connection between any one end and any other end. The second optical switch 62 may switch the combination of optically connected one ends and other ends based on a control signal from an external device, or may switch the combination of optical connections between one end and other ends based on a user operation.

[0068] The second optical switch 62 has two ends optically connected to the other ends of the connecting optical fibers 51a and 51b. The second optical switch 62 has two ends optically connected to the other ends of the connecting optical fibers 51c and 51d. Therefore, the second optical switch 62 can selectively switch the optical connection between the core of the optical fiber 41 or 42 and the core of the optical fiber 43 or 44. In other words, the second optical switch 62 can selectively switch the optical connection between the other end of the core 11 or 12 and the other end of the core 13 or 14.

[0069] Furthermore, the second optical switch 62 selectively optically connects the other end 18 of the core optically connected to the OTDR 20 to the other end 18 of the core 13 or the core 14. For example, when one end 17 of the core 11 is optically connected to the OTDR 20, the second optical switch 62 selectively optically connects the other end 18 of the core 11 to the other end 18 of the core 13 or the core 14. When one end 17 of the core 12 is optically connected to the OTDR 20, the second optical switch 62 selectively optically connects the other end 18 of the core 12 to the other end 18 of the core 13 or the core 14. Therefore, when the selection of one core is switched by the first optical switch 61, the second optical switch 62 can switch from the optical connection between one core and another core before the switching to the optical connection between one core and another core after the switching.

[0070] An operator may switch the first optical switch 61 and switch the second optical switch 62 so as to optically connect one core after the switching to another core. Alternatively, a control unit (not shown) may switch the first optical switch 61 and switch the second optical switch 62 so as to optically connect one core after the switching to another core.

[0071] Next, a crosstalk measurement method for an optical device according to this embodiment will be described. The first connection step S1 is the same as the first connection step S1 according to the first embodiment, and therefore a description thereof will be omitted.

[0072] (Second Connection Step S2) This step is a step of optically connecting the other end 18 of one core other than one of the multiple cores to the other end 18 of the other core selected by the second optical switch 62 via the connecting optical waveguide member 51 including the second optical switch 62. In this step, the other end 18 of the core 11 or core 12 is optically connected to the other end 18 of the core 13 or core 14 via the second optical switch 62. Specifically, the core of the optical fiber 41 or optical fiber 42 and the core of the optical fiber 43 or optical fiber 44 in the fan-in-fan-out device 40 are optically connected via the second optical switch 62.

[0073] In this example, one end 17 of core 11 is optically connected to OTDR 20 via first optical switch 61. Therefore, in this step, the other end 18 of core 11 is optically connected to the other end 18 of core 13 or core 14 via second optical switch 62. In this example, the other end 18 of core 11 is optically connected to the other end 18 of core 13 via second optical switch 62.

[0074] After this step, when light is incident from one end 17 of the core 11, the light passes through the cores of the connecting optical fibers 51a and 51c and enters the core 13 from the other end 18 of the core 13.

[0075] (Measurement step S3) In this step, pulsed incident light output from the OTDR 20 is input from one end 17 of the core 11, and the power of the output light output from one end 17 of the core 11 is measured by the OTDR 20, which includes pulsed light that is a combination of light generated by the incident light crosstalking from the core 11 to the core 13 and light generated by the incident light entering from the core 11 to the core 13 via each core of the connecting optical fibers 51a and 51c crosstalking from the core 13 to the core 11.

[0076] (Processing Step S4) In this step, the power of the measured emitted light is used to determine the crosstalk between the core 11 and the core 13. The method for determining the crosstalk is the same as in the first embodiment, and therefore description thereof will be omitted.

[0077] In the crosstalk measurement method of this embodiment, the second optical switch 62 may be switched and the crosstalk measurement device 1 may measure the crosstalk again. For example, the crosstalk measurement device 1 may optically connect the other end 18 of the core 11 to the other end 18 of the core 14 via the second optical switch 62. In this case, the crosstalk measurement device 1 measures the crosstalk between the core 11 and the core 14.

[0078] Furthermore, in the crosstalk measurement method of this embodiment, the first optical switch 61 may be switched, and the crosstalk measurement device 1 may measure crosstalk again. For example, the OTDR 20 may be optically connected to one end 17 of the core 12 via the first optical switch 61. In this case, the state in which the other end of the core 11 is optically connected to the other end 18 of the core 13 or 14 via the second optical switch 62 is switched to the state in which the other end of the core 12 is optically connected to the other end 18 of the core 13 or 14 via the second optical switch 62. In this case, the crosstalk measurement device 1 measures crosstalk between the core 12 and the core 13 or 14.

[0079] Furthermore, the crosstalk measurement device 1 may include an optical component in at least one of the connecting optical fibers 51a and 51b, such that the loss of light incident from the OTDR 20 side to the second optical switch 62 side is greater than the loss of light incident from the second optical switch 62 side to the OTDR 20 side. In this case, the optical component is disposed closer to the OTDR 20 than the midpoint of the optical path between the other end of the core optically connected to the OTDR 20 and the other end of the core 13 or 14. For example, the optical component may be an isolator, a circulator, or a coupler. The optical component prevents the incident light L from being incident on the midpoint, thereby preventing backscattered light and noise generated from the backscattered light from being superimposed on the crosstalk light CL1. Therefore, the crosstalk measurement device 1 can accurately measure the power of the crosstalk light CL1 and accurately measure crosstalk.

[0080] As described above, the crosstalk measurement method of this embodiment can selectively switch the optical connection between the other end of the optical waveguide optically connected to the OTDR 20 and the other end of any other optical waveguide via the second optical switch 62. Therefore, even if the optical connection between the OTDR and the optical waveguide is switched, the crosstalk measurement method of this embodiment can easily switch the optical connection between the optical waveguide optically connected to the OTDR and another optical waveguide. Therefore, the crosstalk measurement method of this embodiment can easily measure crosstalk.

[0081] Although the present invention has been described above using the above-mentioned embodiments as examples, the present invention is not limited to these.

[0082] For example, the arrangement and number of cores in the multicore fiber 10 may be different from those in the above embodiment. For example, the multicore fiber 10 may include three cores, or may include five or more cores. Furthermore, the multicore fiber 10 may have a trench layer around the core.

[0083] Furthermore, the crosstalk measurement device 1 does not need to have the second optical switch 62. In this case, the other end of the core optically connected to the OTDR and the other end of the other core are optically connected by a connecting optical waveguide. Furthermore, in this case, the multicore fiber 10 may have two cores.

[0084] Furthermore, the crosstalk measurement device 1 does not need to have the first optical switch 61. In this case, the OTDR 20 is optically connected to one of the optical fibers 31 to 34 without the first optical switch 61 being interposed therebetween.

[0085] In the above embodiment, a multi-core fiber has been described as an example of an optical device in which optical waveguides are arranged in parallel, but the optical device of the present invention is not limited to a multi-core fiber. For example, the optical device of the present invention may be applied to an optical fiber cable in which multiple optical fibers are arranged in an array, an optical fiber ribbon in which multiple optical fibers are arranged in a planar array, a multi-element fiber in which multiple bare optical fibers are arranged in a single coating layer, or the crosstalk measurement of an entire transmission system.

[0086] Furthermore, in the above embodiment, for example, as shown in FIG. 5 , the gradient of the power of backscattered light measured by the OTDR 20 is approximately the same in the core 11 and the sections of the connecting optical fibers 51a to 51d. This indicates that the loss of incident light L per unit length due to backscattering is approximately the same in the sections of the core 11 and the connecting optical fibers 51a to 51d. Therefore, in the above embodiment, when light of the same power is propagated through the core 11 and the connecting optical fibers 51a to 51d, the power of the backscattered light per unit length generated in each section is approximately the same. However, when light of the same power is propagated through the core 11 and the connecting optical fibers 51a to 51d, it is preferable that the power of the backscattered light per unit length generated in the connecting optical fibers 51a to 51d is smaller than the power of the backscattered light per unit length generated in each of the cores 11. An example of such connecting optical fibers 51a to 51d is a hollow-core optical fiber whose core is hollow. Alternatively, the connecting optical fibers 51a to 51d may be optical fibers in which the relative refractive index difference of the cores of the connecting optical fibers 51a to 51d is smaller than that of the light propagating through the core of the multicore fiber 10, and the effective cross-sectional area of ​​the propagating light is larger. This is because the power of backscattered light is proportional to the numerical aperture (NA) corresponding to the relative refractive index difference. The ratio of the power of crosstalk light to the power of backscattered light becomes larger, making it easier to detect crosstalk light.

[0087] As described above, according to the present invention, a crosstalk measurement method and a crosstalk measurement device are provided that can easily switch optical paths and measure crosstalk using an OTDR, and it is expected that these will be used in fields such as optical fiber communications.

Claims

1. A crosstalk measurement apparatus for an optical device having a plurality of optical waveguides arranged in parallel with each other, including one end and the other end, comprising: a first optical switch capable of selectively switching one of the plurality of optical waveguides; a connecting optical waveguide that optically connects the other end of the one optical waveguide to the other end of another one of the plurality of optical waveguides; an OTDR (Optical Time Domain Reflectometer) that is optically connected to one end of the one optical waveguide via the first optical switch, and that makes incident light incident on the one end of the one optical waveguide and measures the power of output light output from the one end of the one optical waveguide, including crosstalk light generated when the incident light causes crosstalk between the one optical waveguide and the other one optical waveguide; and a processing unit that calculates crosstalk between the one optical waveguide and the other one optical waveguide using the measured power of the output light.

2. The crosstalk measuring device according to claim 1, characterized in that the plurality of optical waveguides are three or more optical waveguides, and a second optical switch is connected to the connecting optical waveguide, the second optical switch being capable of selectively switching any one of the plurality of optical waveguides other than the one optical waveguide as the other one optical waveguide.

3. The crosstalk measuring device according to claim 2, characterized in that, when the selection of the one optical waveguide is switched by the first optical switch, the second optical switch is capable of switching from an optical connection between the one optical waveguide and the other one optical waveguide before switching to an optical connection between the one optical waveguide and the other one optical waveguide after switching.

4. A crosstalk measuring apparatus for an optical device having three or more optical waveguides arranged in parallel with each other, including one end and the other end, comprising: a connecting optical waveguide including a second optical switch capable of selectively switching any one of the optical waveguides other than one of the optical waveguides, and optically connecting the other end of the one optical waveguide to the other end of the other optical waveguide; an OTDR optically connected to one end of the one optical waveguide, for making incident light incident from the one end of the one optical waveguide, and for measuring the power of outgoing light emitted from the one end of the one optical waveguide, including crosstalk light generated when the incident light crosstalks between the one optical waveguide and the other optical waveguide; and a processing unit that calculates the crosstalk between the one optical waveguide and the other optical waveguide using the measured power of the outgoing light.

5. A crosstalk measurement method for an optical device having a plurality of optical waveguides arranged in parallel with each other, including one end and the other end, comprising: a first connection step of optically connecting an OTDR and one end of the one optical waveguide via a first optical switch capable of selectively switching any one of the plurality of optical waveguides; a second connection step of optically connecting the other end of the one optical waveguide and the other end of another one of the plurality of optical waveguides via a connecting optical waveguide; a measurement step of making incident light output from the OTDR incident from the one end of the one optical waveguide, and measuring the power of output light output from the one end of the one optical waveguide, the output light including crosstalk light generated by the incident light crosstalking between the one optical waveguide and the other one optical waveguide, with the OTDR; and a processing step of determining the crosstalk between the one optical waveguide and the other one optical waveguide using the measured power of the output light.

13. A crosstalk measuring method comprising:

6. A crosstalk measurement method for an optical device having three or more optical waveguides arranged in parallel with each other, each having one end and the other end, comprising: a first connection step of optically connecting an OTDR to one end of one of the optical waveguides; a second connection step of optically connecting the other end of the one optical waveguide to the other end of another optical waveguide selected by a second optical switch via a connection optical waveguide including a second optical switch capable of selectively switching any one of the optical waveguides other than the one optical waveguide; and a measurement step of making an incident light output from the OTDR incident from the one end of the one optical waveguide, and measuring the power of an output light output from the one end of the one optical waveguide, the output light including crosstalk light generated by the incident light crosstalking between the one optical waveguide and the other optical waveguide, with the OTDR; a processing step of determining crosstalk between the one optical waveguide and the other one optical waveguide using the measured power of the emitted light.

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