Crosstalk measuring device and crosstalk measuring 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

[Technical Field]

[0001] The present invention relates to a crosstalk measuring device and a crosstalk measuring method. [Background technology]

[0002] In recent years, the increasing volume of information and communication has necessitated an expansion of optical fiber transmission capacity. Multicore fibers are attracting attention because they can improve space utilization efficiency and enable high-capacity information transmission in limited spaces. 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 need for technology to efficiently evaluate multicore fibers. In particular, crosstalk measurement is an important measurement item for multicore fibers, and since it is not a measurement item for single-core fibers, it is necessary to prepare new measurement equipment.

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

[0004] The crosstalk measurement methods described in Non-Patent Documents 2 and 3 measure the backscattered light after crosstalk, which raises concerns that the power of the light being measured is low, making crosstalk measurement difficult. Crosstalk measurement is even more difficult with multi-core fibers of the type that exhibit low crosstalk.

[0005] On the other hand, the PM method requires light to be incident on one end of a multicore fiber and the light to be received when it exits from the other end. In the OTDR method, it is sufficient to incident light on one end of a multicore fiber and receive the light that exits from the same end. Therefore, there is a need to measure crosstalk using 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 to be measured is to be measured at the other end of a multicore fiber using an optical fiber, and measures the power of the crosstalk light generated by the crosstalk using an OTDR. In this crosstalk measurement method, the OTDR causes incident light to be incident on one end of the predetermined core, and this incident light generates crosstalk light in the other core to which the optical fiber is optically connected, and light containing the crosstalk light incident on the predetermined core is emitted from one end of the predetermined core via the optical fiber. The power of this emitted light is measured by the OTDR. Furthermore, this crosstalk measurement method determines the crosstalk between the predetermined core and the other core based on the measured power of the light.

[0007] [Non-Patent Document 1] 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. [Non-Patent Document 2] 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.2012.6276724 [Non-Patent Document 3] M. 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, 2012 [Non-Patent Document 4] M. 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 [Overview of the project]

[0008] Incidentally, in such a crosstalk measurement method, it is also possible to optically reconnect the OTDR to one end of the other core and incident light onto that end of the other core to generate crosstalk light from the other core to the predetermined core, thereby determining the crosstalk between the other core and the predetermined core.

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

[0010] Therefore, in the above crosstalk measurement method, there is a need to easily switch the optical connection between the OTDR and the core, and to easily switch the optical connection of the core at the other end of the multicore fiber, in order to measure crosstalk. In other words, in the above crosstalk measurement method, there is a need to easily switch the optical path and measure crosstalk.

[0011] Therefore, the present invention aims to provide a crosstalk measuring device and a crosstalk measuring method that can easily switch optical paths and measure crosstalk using an OTDR.

[0012] To solve the above problems, Embodiment 1 of the present invention is a crosstalk measuring device 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 any 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 one of the plurality of optical waveguides; an OTDR optically connected to one end of the one optical waveguide via the first optical switch, which measures the power of the emitted light emitted from one end of the one optical waveguide, including crosstalk light generated when the incident light is incident from the one end of the one optical waveguide and the other optical waveguide is crosstalk by the incident light; and a processing unit that determines the crosstalk between the one optical waveguide and the other optical waveguide using the measured power of the emitted light.

[0013] The crosstalk measurement apparatus of the present 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 apparatus of the present embodiment can easily switch the optical waveguide into which incident light is input from the OTDR. Accordingly, the crosstalk measurement apparatus of the present embodiment can easily switch the optical path using the OTDR to perform crosstalk measurement. Note that, in a pair of optical waveguides whose other ends are optically connected to each other by a connection optical waveguide, the measurement in which light is incident from one end of one optical waveguide to measure the crosstalk between the one optical waveguide and the other optical waveguide, and the measurement in which light is incident from one end of the other optical waveguide to measure the crosstalk between the other optical waveguide and the one optical waveguide have mutually opposite light propagation directions and different optical paths.

[0014] Aspect 2 of the present invention is the crosstalk measurement apparatus according to Aspect 1, characterized in that the plurality of optical waveguides are three or more optical waveguides, and a second optical switch capable of selectively switching any one of the plurality of optical waveguides other than the one optical waveguide as the other one optical waveguide is connected to the connection optical waveguide.

[0015] The crosstalk measurement apparatus of the present 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. Therefore, the crosstalk measurement apparatus of the present embodiment can easily switch the optical connection between the optical waveguide optically connected to the OTDR and the other optical waveguide.

[0016] Aspect 3 of the present invention is the crosstalk measurement apparatus according to Aspect 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 the optical connection between the one optical waveguide before switching and the other one optical waveguide to the optical connection between the one optical waveguide after switching and the other one optical waveguide.

[0017] The crosstalk measurement apparatus of the present embodiment can optically connect the optical waveguide optically connected to the OTDR at the other end to any other optical waveguide, even when the optical waveguide optically connected to the OTDR is switched. Therefore, the crosstalk measurement apparatus of the present embodiment can easily change the combination of optical waveguides for which crosstalk is measured.

[0018] Aspect 4 of the present invention is a crosstalk measurement apparatus for an optical device having three or more parallel optical waveguides each including one end and the other end, the apparatus comprising: a connection optical waveguide that includes a second optical switch capable of selectively switching any one of the plurality of optical waveguides other than one optical waveguide, and optically connects the other end of the one optical waveguide to the other end of another optical waveguide; an OTDR that is optically connected to one end of the one optical waveguide, causes incident light to enter from the one end of the one optical waveguide, and measures the power of outgoing light emitted from the one end of the one optical waveguide, the outgoing light including crosstalk light generated by crosstalk of the incident light between the one optical waveguide and the another optical waveguide; and a processing unit that obtains crosstalk between the one optical waveguide and the another optical waveguide using the measured power of the outgoing light.

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

[0020] Aspect 5 of the present invention is a method for measuring crosstalk in 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 to one end of the plurality of optical waveguides via a first optical switch that can selectively switch any one of the plurality of optical waveguides; a second connection step of optically connecting the other end of the one optical waveguide to the other end of one of the plurality of optical waveguides via a connecting optical waveguide; and from the OTDR The crosstalk measurement method is characterized by comprising: a measurement step of measuring the power of the emitted light emitted from one end of one optical waveguide using the OTDR, including crosstalk light generated when the emitted light crosstalks between the one optical waveguide and the other 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 emitted light.

[0021] The crosstalk measurement method in this embodiment allows for selective switching of the optical connection between the OTDR and one end of any optical waveguide via a first optical switch. Therefore, the crosstalk measurement method in this embodiment allows for easy switching of the optical waveguide into which incident light is received from the OTDR. Consequently, the crosstalk measurement method in this embodiment allows for easy switching of optical paths and measurement of crosstalk using the OTDR.

[0022] Aspect 6 of the present invention is a method for measuring crosstalk in an optical device having three or more optical waveguides arranged in parallel with respect to one end and the other end of each other, comprising: a first connection step of optically connecting an OTDR to one end of one of the plurality of optical waveguides; and a second connection step of optically connecting the other end of the one optical waveguide to the other optical waveguide selected by the second optical switch via a connecting optical waveguide including a second optical switch that can selectively switch any of the plurality of optical waveguides other than the one optical waveguide. A crosstalk measurement method comprising: a connection step; a measurement step in which incident light emitted from the OTDR is incident on one end of the one optical waveguide, and the power of the emitted light emitted from one end of the one optical waveguide is measured by the OTDR, including crosstalk light generated when the incident light crosstalks between the one optical waveguide and the other optical waveguide; and a processing step in which the crosstalk between the one optical waveguide and the other optical waveguide is determined using the measured power of the emitted light.

[0023] The crosstalk measurement method in 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 a second optical switch. Therefore, the crosstalk measurement method in this embodiment can easily switch the optical connection between the optical waveguide optically connected to the OTDR and other optical waveguides. Thus, the crosstalk measurement method in this embodiment can easily switch optical paths and measure crosstalk using the OTDR.

[0024] As described above, the present invention provides a crosstalk measuring device and a crosstalk measuring method that can easily switch optical paths using an OTDR and measure crosstalk. [Brief explanation of the drawing]

[0025] [Figure 1] This figure shows a cross-section perpendicular to the longitudinal direction of a multicore fiber according to the first embodiment of the present invention. [Figure 2]This figure shows a crosstalk measuring device in the first embodiment. [Figure 3] This is a flowchart showing the procedure for the crosstalk measurement method in the first embodiment of the present invention. [Figure 4] Figure 2 shows the propagation of light in the crosstalk measurement device. [Figure 5] This figure shows the measurement results from OTDR. [Figure 6] This is a magnified view of a portion of Figure 5. [Figure 7] This figure shows a crosstalk measuring device in the second embodiment. [Modes for carrying out the invention]

[0026] The following examples illustrate embodiments for implementing the crosstalk measurement method and crosstalk measurement apparatus according to the present invention, with reference to the accompanying drawings. The embodiments illustrated below are provided to facilitate understanding of the present invention and are not intended to limit its interpretation. The present invention can be modified and improved from the following embodiments within the scope of the claims without departing from its spirit. Note that in the drawings referenced below, the dimensions of each component may be shown differently for the sake of clarity.

[0027] (First Embodiment) Figure 1 shows a cross-section of the multicore fiber of this embodiment perpendicular to the longitudinal direction. The multicore fiber 10 has a plurality of cores 11 to 14 capable of transmitting light, and a cladding 15 surrounding the outer circumferential surface of each of the cores 11 to 14. The outer circumferential surface of the cladding 15 may be surrounded by a coating layer made of resin.

[0028] Each of the cores 11-14 has one end and the other end, and they are arranged in parallel with each other along the longitudinal direction of the multicore fiber 10. The refractive index of the cores 11-14 is higher than that of the cladding 15, and each of the cores 11-14 is capable of transmitting light. Therefore, each of the cores 11-14 is an optical waveguide, and the multicore fiber 10 is an optical device having multiple optical waveguides arranged in parallel with each other.

[0029] In this embodiment, cores 11-14 are made of silica glass to which a dopant that increases the refractive index, such as germanium (Ge), is added, and cladding 15 is made of silica glass without any additives. For example, cores 11-14 may be made of silica glass without any additives, and cladding 15 may be made of silica glass to which a dopant that decreases the refractive index, such as fluorine (F), or cores 11-14 may be made of silica glass to which a dopant that increases the refractive index is added, and cladding 15 may be made of silica glass to which a dopant that decreases the refractive index is added. Furthermore, the dopant that increases the refractive index and the dopant that decreases the refractive index are not particularly limited.

[0030] Next, a crosstalk measurement device in the optical device of this embodiment will be described. Figure 2 is a diagram showing the crosstalk measurement device in this embodiment. As shown in Figure 2, the crosstalk measurement device 1 of 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 the multicore fiber 10. The multicore fiber 10 has one end 17 and the other end 18. In the following description, one end 17 and the other end 18 may also be described as one end 17 and the other end 18 of cores 11 to 14.

[0031] The OTDR20 is used in conjunction with optical fibers, etc., and emits pulsed light to measure the power of light incident from the multicore fiber 10, and to measure the time from the emission of pulsed light until the light to be measured is incident. It is a device that can measure optical losses such as transmission loss, bending loss, and connection loss in optical fibers, detect breaks in optical fibers, and measure the amount of light reflected. In this embodiment, the first optical switch 61 is optically connected to the OTDR20 via an optical fiber.

[0032] The first optical switch 61 has one end and a plurality of other ends. The first optical switch 61 selectively switches the optical connection between one end and any of the other ends by switching internal waveguides. The first optical switch 61 may switch the optical connection between one end and any of the other ends based on a control signal from a control unit (not shown), or it may switch the optical connection between one end and any 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 the optical fibers 31 to 34 of the fan-in-fan-out device 30, respectively. 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 between them.

[0034] The fan-in-fan-out device 30 includes a plurality of optical waveguides (not shown) that can be individually optically connected to cores 11-14 at one end 17 of the multicore fiber 10, and optical fibers 31-34, each containing a core individually optically connected to the respective optical waveguide. In this example, one end 17 of cores 11-14 and the cores of optical fibers 31-34 are optically connected, 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 11-14 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 similar configuration to the fan-in / fan-out device 30, and the cores of optical fibers 41-44 are individually optically connected to multiple optical waveguides (not shown) that can be individually optically connected to the cores 11-14 of the multicore fiber 10. In this example, the other ends 18 of cores 11-14 are optically connected to the cores of optical fibers 41-44, 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, for example, single-mode fibers. One end of each connecting optical fiber 51a to 51d is connected to optical fibers 41 to 44.

[0037] The second optical switch 62 has one end and a plurality of other ends. The second optical switch 62 selectively switches the optical connection between one end and any of the other ends by switching internal waveguides. The second optical switch 62 may switch the optical connection between one end and any of the other ends based on a control signal from a control unit (not shown), or it may switch the optical connection between one end and any 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 optical fiber 41 and any of the cores of optical fibers 42 to 44. In other words, the second optical switch 62 can selectively switch the optical connection between 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 core 11 to the other end of any of the cores 12 to 14, and a second optical switch 62 is connected to the connecting waveguide. It is preferable that the second optical switch 62 is provided at a point other than the midpoint of the optical path from the other end 18 of core 11 to the other end 18 of cores 12 to 14. For this reason, for example, the length of the connecting optical fiber 51a is 1 km, and the lengths of the connecting optical fibers 51b to 51d are 10 km.

[0040] The OTDR20 is connected to the processing unit 25, and data related to the power of the light received by the OTDR20 is output to the processing unit 25. The processing unit 25 is a computing device that uses the light power measured by the OTDR20 to determine the crosstalk. The processing unit 25 can use integrated circuits such as a microcontroller, IC (Integrated Circuit), LSI (Large-scale Integrated Circuit), ASIC (Application Specific Integrated Circuit), or NC (Numerical Control) device. Furthermore, if an NC device is used for the processing unit 25, it may use a machine learning machine or not. When the processing unit 25 receives data related to the light power from the OTDR20, it uses this data to determine the crosstalk between core 11 and one of cores 12-14, as described later, and outputs the data related to the determined crosstalk. Note that the processing unit 25 and the OTDR20 may be housed in a single enclosure, and some components may be shared. Furthermore, the components constituting the processing unit 25 may also serve as a control unit (not shown) that controls the switching of the first optical switch 61 and the second optical switch 62.

[0041] Next, a crosstalk measurement method in the optical device of this embodiment will be described. Figure 3 is a flowchart showing the procedure of the crosstalk measurement method in this embodiment. As shown in Figure 3, the crosstalk measurement method of this embodiment comprises 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, the multicore fiber 10, which will be used as the optical device to be measured, is prepared and set in the crosstalk measurement device 1. The length of the multicore fiber 10 is, for example, 21 km.

[0043] This step involves optically connecting the core to one end 17 of any one of the cores 11 to 14 via the first optical switch 61. In this step, the OTDR20 is optically connected to one of the cores 11 to 14 via the first optical switch 61. Specifically, the OTDR20 is optically connected to 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. Thus, the OTDR20 and the core of the optical fiber 31 are optically connected via the first optical switch 61. Thus, the OTDR20 and core 11 are optically connected.

[0044] (Second connection step S2) This step involves optically connecting the other end 18 of one core to the other end 18 of one of the cores 12-14 via a connecting optical waveguide. In this step, the other end 18 of core 11 is optically connected to the other end 18 of any of the cores 12-14 via a 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 the core of any of the optical fibers 42-44. Therefore, in this step, the other end of core 11 to which the OTDR 20 is optically connected is optically connected to the other end of any of the cores 12-14 via the second optical switch 62. Thus, the second optical switch 62 can selectively switch to any of the optical waveguides other than the one optical waveguide that is 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 which is connected to the connecting optical fiber 51b. As a result, the core of the connecting optical fiber 51a and the core of the connecting optical fiber 51b are optically connected via the second optical switch 62. Consequently, the other end 18 of core 11 and the other end 18 of core 12 are optically connected via the second optical switch 62.

[0046] After this step, if light enters from one end 17 of the core 11, the light enters the core 12 from the other end 18 of the core 12 via the respective cores of the connecting optical fibers 51a and 51b.

[0047] (Measurement step S3) This step involves having incident light emitted from the OTDR20 enter one end 17 of one core, and measuring the power of the emitted light emitted from one end 17 of one core, including the crosstalk light generated by the crosstalk between the one core and the other core, using the OTDR20. As described above, the OTDR20 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, pulsed incident light emitted from the OTDR20 is introduced into the core 11 from one end 17, and the power of the emitted light emitted from one end 17 of the core 11 is measured by the OTDR20, which includes pulsed light resulting from the crosstalk between the incident light from the core 11 to the core 12 and the crosstalk between the incident light entering the core 11 from the core 12 via the connecting optical waveguide member 51 and the core 11.

[0048] Figure 4 shows the propagation of light in the crosstalk measurement device shown in Figure 2. The above will be explained in detail using this figure. Note that in Figure 4, the fan-in-fan-out devices 30 and 40 are shown in a simplified manner. Also, the connecting optical fibers 51c and 51d are 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 being able to stably perform the crosstalk measurement described later, more preferably 3 nm or more, and even more preferably 5 nm or more. Also, 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 pulse width of the light emitted from the OTDR 20 is appropriately adjusted so that the emitted light, including the crosstalk light described later, does not saturate. In this case, an attenuator may be interposed between the OTDR 20 and the optical fiber 31.

[0049] The pulsed light emitted from the OTDR20 enters the core 11 as incident light from one end 17 to the other end 18 of the core 11. The pulsed incident light propagating through the core 11 propagates from the core 11 to the core 12 while crosstalking. Because the incident light L is pulsed, the crosstalk light CL1 that crosstalks from the core 11 to the core 12 is also pulsed and propagates from one end 17 to the other end 18 of the core 12, roughly parallel to the incident light L. During this time, because of the crosstalk from the core 11 to the core 12, the power of the incident light L decreases in proportion to the distance it propagates through the core 11, and the power of the crosstalk light CL1 increases in proportion to the distance it propagates through the core 12. Since 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 roughly simultaneously.

[0050] Next, the incident light L and the crosstalk light CL1 enter the cores of the connecting optical fiber 51a and 51b, respectively, approximately simultaneously via the fan-in-fan-out device 40. The incident light L entering the core of the connecting optical fiber 51a and the crosstalk light CL1 entering the core of the connecting optical fiber 51b pass each other approximately at the midpoint of the optical path between the other end 18 of core 11 and the other end 18 of core 12, i.e., the connecting optical waveguide. The incident light L reaches the end of the connecting optical fiber 51b, and approximately simultaneously, 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 enters core 12 from the other end 18, and the crosstalk light CL1 enters core 11 from the other end 18. At this time, the incident light L and the crosstalk light CL1 enter cores 12 and 11, respectively, approximately simultaneously. Even if the lengths of the optical fibers 41 and 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, respectively, approximately simultaneously.

[0051] The incident light L that enters core 12 and the crosstalk light CL1 that enters core 11 propagate through cores 12 and 11 towards one end 17, generally in parallel. During this time, the incident light L propagating through core 12 also propagates through core 11 while crosstalking with it. Therefore, the light crosstalking from core 12 to core 11 combines with the crosstalk light CL1 propagating through core 11. The combined light is pulsed and propagates while gradually increasing in power. From one end 17 of core 11, the emitted light is a combination of the pulsed crosstalk light CL1 and light such as backscattered light. Therefore, the emitted light includes the pulsed crosstalk light CL1.

[0052] The light emitted from the core 11 is incident on the OTDR20 via the fan-in-fan-out device 30, received by the OTDR20, and its power is measured by the OTDR20.

[0053] Figure 5 shows the measurement results of the emitted light received by the OTDR20. In Figure 5, the horizontal axis represents the propagation distance of the incident light L, and the vertical axis represents the power of the emitted light received by the OTDR20. The vertical axis in Figure 5 shows the power of the emitted light in decibels as a ratio to a predetermined power set for the OTDR20. For example, if this predetermined power is 1 mW, the unit of the vertical axis may be dBm. In addition, in the measurement obtained to obtain Figure 5, core 11 and core 12 were connected by an optical fiber as a connecting optical waveguide member in order to reproduce the state in which the second optical switch 62 optically connects core 11 and core 12. As shown in Figure 5, in the section in which the incident light L propagates through core 11 and the section in which the incident light L propagates through core 12, backscattered light is measured as emitted light. The slope of the line showing the emitted light in these sections indicates the loss of incident light L per unit length due to backscattering. Furthermore, pulsed light was measured at the boundary between the core 11 section and the connecting optical waveguide member 51 section, and at the boundary between the connecting optical waveguide member 51 section and the core 12 section. This light indicates reflection from the fan-in-fan-out device 40, etc. Also, pulsed light was measured on the core 11 side of the midpoint of the connecting optical waveguide member 51. This light indicates reflection from the second optical switch 62.

[0054] A 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 pass each other approximately at the midpoint of the optical path, so this pulsed light represents the crosstalk light CL1. In addition, backscattered light is measured as emitted light in the section in which 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 shown above, a pulse indicating the power of the crosstalk light CL1 is shown approximately at 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 interfering with the end of the connecting optical waveguide member 51, it is preferable that the optical path length of the connecting optical waveguide member 51 be longer than the half-width of the incident light L. In other words, the total length should be L SCF Let ΔT be the half-width of the incident light L. pulse When the refractive index of the cores of the connecting optical fibers 51a and 51b is n and the high speed is c, it is preferable that the following equation is satisfied. L SCF >ΔT pulse ×c / n

[0056] Furthermore, it is more preferable that the following equation is satisfied, from the viewpoint of further suppressing the influence of the end of the connecting optical waveguide member 51 on the pulse. L SCF >1.2 × ΔT pulse ×c / n

[0057] The OTDR20 outputs data related to the power of the measured emitted light to the processing unit 25.

[0058] (Processing step S4) This step involves determining the crosstalk between one core and another core using the measured power of the emitted light. In this step, the crosstalk between core 11 and core 12 is determined using the measured power of the emitted light. Figure 6 is an enlarged view of the emitted light measured approximately at the midpoint in Figure 5. As described above, backscattered light is also generated in the connecting optical waveguide member 51. Therefore, in regions other than the region where pulsed light is shown, the power of this backscattered light is measured. So, the processing unit 25 first calculates the power of the backscattered light P in the region where pulsed light is shown from the power of the emitted light in the region other than the region where pulsed light including crosstalk light CL1 is shown, based on the data input from OTDR 20. BSis determined. Specifically, the processing unit 25 performs, for example, linear approximation on the power of the emitted light in a region other than the region where the pulsed light is shown, to obtain the power P of the backscattered light BS is determined. Next, the processing unit 25 determines the power P of the emitted light in the region where the pulsed light is shown OUT and the determined power P of the backscattered light BS are subtracted to obtain the difference. 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 power P of crosstalk in each of the fan-in fan-out devices 30 and 40 XT_FIFO . The power P XT_FIFO is negligibly small, the power of the pulsed light may be taken as the power P of the crosstalk light CL1 XT-MCF . However, it is preferable from the viewpoint of more accurately obtaining the power P XT_FIFO that the power obtained by removing the power P from the power of the pulsed light is taken as the power P of the crosstalk light CL1 XT_MCF XT_MCF . It is also preferable from the viewpoint of more accurately obtaining the power P XT_MCF to further consider the insertion loss of the second optical switch 62.

[0059] The power P XT_FIFO can 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. As a result, the length of the multi-core fiber 10 is set to 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 and 42 and the connecting optical waveguide member 51 OUT includes the power P XT_FIFO and the power P BS . Therefore, the power P can be obtained by calculating the difference between the power P OUT and the power P BS in the same manner as described above XT_FIFO .

[0060] ​The processing unit 25 calculates the power P of the crosstalk light CL1. XT_MCF The crosstalk is converted to an output. At this time, the processing unit 25 may convert the crosstalk to decibels, which represent the ratio of the power of the incident light L emitted from one end 17 of the core 12, and output it. Alternatively, the processing unit 25 may convert it to decibels, which represent the ratio to a predetermined power defined in the OTDR20 shown in Figures 5 and 6, and output it. In this way, the crosstalk is obtained.

[0061] In the crosstalk measurement method of this embodiment, the selection of cores 11 to 14 by the first optical switch 61 may be switched, and the crosstalk measuring device 1 may measure the crosstalk again. For example, the first optical switch 61 is switched to optically connect the OTDR 20 and one end 17 of core 12. That is, the optical path through which the 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 the 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 takes the arithmetic mean of the light power distribution from core 11 to core 12 measured in measurement step S3 and the inverted light power distribution. In this way, the power of the light that is backscattered when the core 11 propagates from one end 17 to the other end 18, and the power of the light that is backscattered when the core 11 propagates from the other end 18 to the one end 17 are averaged out, and the slope of the light power distribution in the range of the core 11 in Figure 5 is almost eliminated. Similarly, the slope of the light power distribution in the range of the core 12 in Figure 5, and the slope of the light power distribution in the range of the connecting optical waveguide member 51 are almost eliminated. In addition, approximately at the midpoint of the optical path between the other end 18 of the core 11 and the other end 18 of the core 12, a pulsed crosstalk light appears, which is the average of the crosstalk light CL1 and the crosstalk light measured in that state. The processing unit 25 determines the crosstalk from the power of the averaged pulsed crosstalk light.

[0062] Furthermore, in the crosstalk measurement method of this embodiment, the selection of cores 12 to 14 by the second optical switch 62 may be switched, and the crosstalk measurement device 1 may measure the crosstalk again. For example, the second optical switch 62 is switched to optically connect the other end 18 of core 11 and the other end 18 of core 13. In other words, the optical path through which the incident light from 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 determines the crosstalk between core 11 and core 13 based on the measured power.

[0063] Furthermore, in the crosstalk measurement method of this embodiment, both the selection of cores 11-14 by the first optical switch 61 and the selection of cores 12-14 by the second optical switch 62 may be switched, and the crosstalk measuring device 1 may measure the crosstalk. 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 the cores other than the core selected by the first optical switch 61.

[0064] Furthermore, the crosstalk measuring 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 positioned on the core 11 side of the midpoint of the optical path between the other end of the core 11 and any other end of the cores 12 to 14. For example, the optical component may be an isolator, a circulator, or a coupler. The optical component suppresses the incident light L from being incident at the midpoint, and the superposition of backscattered light and noise generated from backscattered light onto the crosstalk light CL1 can be suppressed. Therefore, the crosstalk measuring 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 apparatus 1 of this embodiment, the optical connection between the OTDR 20 and one end of any one core can be selectively switched via the first optical switch 61. Therefore, the crosstalk measurement method and crosstalk measurement apparatus 1 of this embodiment can easily switch the core into which the 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 one other core via the second optical switch 62. Therefore, the crosstalk measurement method and crosstalk measurement apparatus 1 of this embodiment can easily switch the optical connection between one core optically connected to the OTDR and another core. Thus, 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. Note that, unless otherwise specified, redundant descriptions of components identical or equivalent to those in the first embodiment will be omitted. 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] In the example shown in Figure 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 selectively switches the optical connection between any one-end and any other-end by switching its internal waveguides. 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 it may switch the combination of optical connections between one-ends and other-ends by user operation.

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

[0069] Furthermore, the second optical switch 62 selectively optically connects the other end 18 of a core optically connected to the OTDR 20 to the other end 18 of core 13 or core 14. For example, if one end 17 of core 11 is optically connected to the OTDR 20, the second optical switch 62 selectively optically connects the other end 18 of core 11 to the other end 18 of core 13 or core 14. Also, if one end 17 of core 12 is optically connected to the OTDR 20, the second optical switch 62 selectively optically connects the other end 18 of core 12 to the other end 18 of core 13 or 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 switch to the optical connection between one core and another core after the switch.

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

[0071] Next, a method for measuring crosstalk in the optical device of this embodiment will be described. The first connection step S1 is the same as the first connection step S1 in the first embodiment, so its explanation will be omitted.

[0072] (Second connection step S2) This step involves optically connecting one of the cores (excluding one of the multiple cores) to the other end 18 of the other core selected by the second optical switch 62 via a connecting optical waveguide member 51 including a second optical switch 62. In this step, the other end 18 of core 11 or core 12 is optically connected to the other end 18 of core 13 or core 14 via the second optical switch 62. Specifically, the core of optical fiber 41 or optical fiber 42 and the core of 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 the core 11 is optically connected to the OTDR 20 via the first optical switch 61. Therefore, in this step, the other end 18 of the core 11 is optically connected to the other end 18 of the core 13 or core 14 via the second optical switch 62. In this example, the other end 18 of the core 11 is optically connected to the other end 18 of the core 13 via the second optical switch 62.

[0074] After this step, if light enters from one end 17 of the core 11, the light enters the core 13 from the other end 18 of the core 13 via the respective cores of the connecting optical fibers 51a and 51c.

[0075] (Measurement step S3) In this step, pulsed incident light emitted from the OTDR20 is introduced into the core 11 from one end 17, and the power of the emitted light emitted from one end 17 of the core 11 is measured by the OTDR20. This light includes the light generated by the crosstalk between the incident light from the core 11 to the core 13 and the light generated by the crosstalk between the incident light entering the core 13 from the core 13 via the respective cores of the connecting optical fibers 51a and 51c, and then emitted from the core 11 to the core 11.

[0076] (Processing step S4) In this step, the crosstalk between core 11 and core 13 is determined using the measured power of the emitted light. The method for determining the crosstalk is the same as in the first embodiment, so a description is omitted.

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

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

[0079] Furthermore, the crosstalk measuring device 1 may have an optical component in at least one of the connecting optical fibers 51a and 51b in which 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 positioned on the OTDR 20 side of 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 suppresses the incident light L from being incident at the midpoint, and can suppress the superposition of backscattered light and noise generated from backscattered light onto the crosstalk light CL1. Therefore, the crosstalk measuring 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 when the optical connection between the OTDR and the optical waveguide is switched, the optical connection between the optical waveguide optically connected to the OTDR and the other optical waveguide can be easily switched. Thus, the crosstalk measurement method of this embodiment can easily measure crosstalk.

[0081] Although the present invention has been described above with reference to the above embodiments, the present invention is not limited to these.

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

[0083] Furthermore, the crosstalk measuring device 1 does not necessarily have a 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. Also in this case, the multicore fiber 10 may have two cores.

[0084] Furthermore, the crosstalk measuring device 1 does not necessarily have to have the first optical switch 61. In this case, the OTDR 20 is optically connected to any of the optical fibers 31 to 34 without going through the first optical switch 61.

[0085] Furthermore, although the above embodiment described a multicore fiber as an example of an optical device in which optical waveguides are arranged in parallel, the optical device of the present invention is not limited to a multicore fiber. For example, it can be applied to optical fiber cables in which multiple optical fibers are arranged in a line, optical fiber tapes in which multiple optical fibers are arranged in a planar manner, multi-element fibers in which multiple bare optical fibers are arranged in a single coating layer, and crosstalk measurement of an entire transmission system.

[0086] Furthermore, in the above embodiment, as shown in Figure 5 for example, the slope of the power of the backscattered light measured by the OTDR20 is approximately the same in the section between the core 11 and 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 section between 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. Examples of such connecting optical fibers 51a to 51d include hollow-core optical fibers in which the core is hollow. Alternatively, the connecting optical fibers 51a to 51d may be optical fibers in which the difference in relative refractive index between 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 difference in relative refractive index. The ratio of the power of crosstalk light to the power of backscattered light becomes larger, making it easier to detect the crosstalk light.

[0087] As described above, the present invention provides a crosstalk measurement method and a crosstalk measurement apparatus that can easily switch optical paths and measure crosstalk using an OTDR, and is expected to be used in fields such as optical fiber communication.

Claims

1. A crosstalk measuring device for an optical device having a plurality of optical waveguides arranged in parallel with each other, including one end and the other end, A first optical switch capable of selectively switching one of the aforementioned plurality of optical waveguides, A connecting optical waveguide that optically connects the other end of one of the aforementioned optical waveguides to the other end of one of the plurality of optical waveguides, An Optical Time Domain Reflectometer (OTDR) is optically connected to one end of the optical waveguide via the first optical switch, and measures the power of the emitted light emitted from one end of the optical waveguide, including crosstalk light generated when the incident light crosstalks between the optical waveguide and the other optical waveguide, and which receives incident light from the one end of the optical waveguide. A processing unit that uses the measured power of the emitted light to determine the crosstalk between one optical waveguide and the other optical waveguide, Equipped with, The aforementioned plurality of optical waveguides are three or more optical waveguides, A second optical switch is connected to the aforementioned connecting optical waveguide, which is capable of selectively switching any of the multiple optical waveguides other than the one mentioned above to be the other optical waveguide. A crosstalk measuring device characterized by the following features.

2. The second optical switch is capable of switching from the optical connection between the first optical waveguide and the other optical waveguide before the switch, to the optical connection between the first optical waveguide and the other optical waveguide after the switch, when the selection of one optical waveguide is switched by the first optical switch. The crosstalk measuring device according to feature 1.

3. A crosstalk measuring device for an optical device having three or more optical waveguides arranged in parallel with each other, including one end and the other end, The optical waveguide includes a second optical switch capable of selectively switching any of the optical waveguides other than one of the plurality of optical waveguides, and a connecting optical waveguide that optically connects the other end of one optical waveguide to the other optical waveguide. An OTDR is optically connected to one end of the aforementioned optical waveguide, and measures the power of the emitted light emitted from one end of the aforementioned optical waveguide, including crosstalk light generated when the incident light crosstalks between the aforementioned optical waveguide and the other optical waveguide, and which is incident light received from the aforementioned end of the aforementioned optical waveguide. A processing unit that uses the measured power of the emitted light to determine the crosstalk between one optical waveguide and the other optical waveguide, Equipped with A crosstalk measuring device characterized by the following features.

4. A method for measuring crosstalk in an optical device having three or more optical waveguides arranged in parallel with each other, including one end and the other end, A first connection step involves optically connecting the OTDR to one end of one of the multiple optical waveguides, A second connection step involves optically connecting the other end of one optical waveguide to the other optical waveguide selected by the second optical switch via a connecting optical waveguide that includes a second optical switch capable of selectively switching any of the optical waveguides other than the one optical waveguide among the plurality of optical waveguides, A measurement step of measuring the power of the emitted light emitted from one end of one optical waveguide, including crosstalk light generated by crosstalk between the one optical waveguide and the other optical waveguide, by the OTDR, with the OTDR. A processing step of determining the crosstalk between one optical waveguide and the other optical waveguide using the measured power of the emitted light, Equipped with A crosstalk measurement method characterized by the following features.

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