Crosstalk measuring method, and crosstalk measuring device

Abstract

This crosstalk measuring method includes: a connecting step S1 for optically connecting an end 18 of a core 11 and an end 18 of a core 12 by way of a core of a first optical fiber 51; a first measuring step S2 for using an optical time domain reflectometer (OTDR) 20 to measure a power of emitted light emitted from one end 17 of the core 11, the emitted light including pulsed crosstalk light CL1 obtained through a combination of light generated when pulsed incident light L from the OTDR 20 is caused to enter from the one end 17 of the core 11 and crosstalk of the incident light L from the core 11 to the core 12 occurs, and light generated when crosstalk, from the core 12 to the core 11, of the incident light L that has entered the core 12 from the core 11 occurs; and a processing step S3 for using the measured power of the emitted light to obtain the magnitude of the crosstalk between the core 11 and the core 12.

Description

Crosstalk measurement method and crosstalk measurement device

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

[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] [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.[2] M. Ohashi, K. Kawazu, A. Nakamura, and Y. Miyoshi, “Simple backscattered power technique for measuring crosstalk of multi-core fibers,” OptoElectronics and Communications Conference, Busan, South Korea, P1-25, 2012, DOI: https: / / doi.org / 10.1109 / OECC.2012.6276724[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

[0005] The PM method requires that light be incident on one end of a multicore fiber and that the light exiting from the other end be received. In contrast, the OTDR method requires that light be incident on one end of a multicore fiber and that the light exiting from the end be received. For this reason, there is a need to measure crosstalk using the OTDR method. However, the crosstalk measurement methods described in Non-Patent Documents 2 and 3 measure backscattered light of light after crosstalk, which raises concerns that the power of the measured light is low, making crosstalk measurement difficult. Crosstalk measurement is even more difficult in multicore fibers with low crosstalk. However, as described above, there is a need to measure crosstalk using the OTDR method. Such a need may arise not only for multicore fibers but also for optical devices having multiple optical waveguides in which crosstalk may occur.

[0006] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a crosstalk measuring method and a crosstalk measuring device that can easily measure crosstalk using the OTDR method.

[0007] In order to solve the above-mentioned problems, a first aspect of the present invention is a method for measuring crosstalk in an optical device having a first optical waveguide and a second optical waveguide which are arranged in parallel and include one end and the other end, the method comprising: a connecting step of optically connecting the other end of the first optical waveguide and the other end of the second optical waveguide via a first connecting optical waveguide; and light generated when the incident light, which is incident from the first optical waveguide to the second optical waveguide via an optical waveguide, crosstalks from the second optical waveguide to the first optical waveguide, and the light includes pulsed light generated when the incident light is incident from the first optical waveguide to the second optical waveguide via an optical waveguide, the pulsed light including pulsed light being combined, the pulsed light including pulsed light being combined from the incident light and the light generated when the incident light is incident from the second optical waveguide to the first optical waveguide, the pulsed light including pulsed light being combined

[0008] Pulsed incident light propagating from one end of the first optical waveguide to the other end propagates from the first optical waveguide to the second optical waveguide while crosstalking. Therefore, crosstalk light that crosstalks from the first optical waveguide to the second optical waveguide also becomes pulsed and propagates from one end to the other end of the second optical waveguide while traveling generally parallel to the incident light. The incident light that reaches the other end of the first optical waveguide enters the first connecting optical waveguide. Furthermore, the pulsed crosstalk light that propagates from one end of the second optical waveguide to the other end of the second optical waveguide enters the first connecting optical waveguide from the opposite side to the incident light. Because the speed of light within an optical device is constant, the propagation speed of the incident light and the propagation speed of the crosstalk light are equal to each other. Therefore, the incident light and the crosstalk light reach the other ends of the first optical waveguide and the second optical waveguide approximately simultaneously, and the incident light and the crosstalk light intersect approximately at the midpoint of the first connecting optical waveguide. Then, the incident light enters the second optical waveguide from the other end of the second optical waveguide, and the crosstalk light enters the first optical waveguide from the other end of the first optical waveguide. At this time, the timing at which the incident light enters the second optical waveguide and the timing at which the crosstalk light enters the first optical waveguide are approximately the same. Therefore, the crosstalk light propagates from the other end to one end of the first optical waveguide while traveling approximately parallel to the incident light propagating from the other end to one end of the second optical waveguide. During this time, the incident light propagating through the second optical waveguide propagates while crosstalking with the first optical waveguide. Therefore, light that crosstalks from the second optical waveguide to the first optical waveguide is combined with the crosstalk light propagating through the first waveguide. The combined light is pulsed, and the output light that exits from one end of the first optical waveguide contains pulsed light generated by the crosstalk. The light that exits the first optical waveguide is received by an OTDR, and the power of the output light is measured. The measured power of the output light is used to determine the magnitude of the crosstalk between the first optical waveguide and the second optical waveguide.

[0009] As described above, the crosstalk measurement method of this embodiment uses an OTDR to measure light that crosstalks into other optical waveguides, and therefore the power of the crosstalk light is greater than when detecting backscattered light from the crosstalked light as in Patent Documents 2 and 3. Furthermore, in the crosstalk measurement method of this embodiment, crosstalk light generated when the incident light propagates from one end of the first optical waveguide to the other end and crosstalk light generated when the incident light propagates from the other end of the second optical waveguide to one end are combined, so the power of the pulsed light generated by the crosstalk tends to be greater. Therefore, the crosstalk measurement method of this embodiment makes it easy to measure crosstalk.

[0010] A second aspect of the present invention is the crosstalk measuring method according to the first aspect, wherein the length of the first connection optical waveguide is longer than the half-width of the incident light.

[0011] As described above, the incident light and the crosstalk light intersect at approximately the midpoint of the first connection optical waveguide. Therefore, in the OTDR, the pulsed light generated by the crosstalk appears to be generated at approximately the midpoint of the first connection optical waveguide. Furthermore, the pulse width of the incident light and the pulse width of the crosstalk light are approximately the same. Therefore, according to the crosstalk measurement method of this aspect, it is possible to suppress the influence of noise such as reflection at the end of the first connection optical waveguide on the output light including the pulsed crosstalk light, thereby enabling more accurate measurement of crosstalk.

[0012] A third aspect of the present invention is the crosstalk measurement method according to the first or second aspect, further comprising a second measuring step of measuring, with the OTDR, a power of the output light output from the one end of the second optical waveguide, the power of the output light including pulsed light generated by combining pulsed incident light output from the OTDR into one end of the second optical waveguide, the light being generated as a result of crosstalk of the incident light from the second optical waveguide to the first optical waveguide, and light being generated as a result of crosstalk of the incident light, which is input from the second optical waveguide to the first optical waveguide via the first connecting optical waveguide, into the first optical waveguide,

[0013] In this case, the crosstalk light generated by propagating incident light from the first optical waveguide to the second optical waveguide and the crosstalk light generated by propagating incident light from the second optical waveguide to the first optical waveguide are used. Therefore, compared to the case where only the crosstalk light generated by propagating incident light from the first optical waveguide to the second optical waveguide is used, errors can be suppressed and the crosstalk can be determined more accurately.

[0014] A fourth aspect of the present invention is the crosstalk measurement method of the third aspect, characterized in that in the processing step, the magnitude of the crosstalk between the first optical waveguide and the second optical waveguide is determined using the result of averaging the power of the output light measured in the first measurement step and the power of the output light measured in the second measurement step.

[0015] By using such an averaging process, the magnitude of the crosstalk can be easily and accurately determined.

[0016] A fifth aspect of the present invention is the crosstalk measuring method according to any one of the first to fourth aspects, wherein the wavelength width of the incident light is 1 nm or more.

[0017] In this case, the error in the power of the emitted light measured by the OTDR can be reduced.

[0018] A sixth aspect of the present invention is the crosstalk measurement method according to any one of the first to fifth aspects, characterized in that the OTDR and the first optical waveguide, the first optical waveguide and the first connecting optical waveguide, and the first connecting optical waveguide and the second optical waveguide are optically connected by a fan-in-fan-out device, and the processing step removes the magnitude of crosstalk in the fan-in-fan-out device and determines the magnitude of the crosstalk between the first optical waveguide and the second optical waveguide.

[0019] In this case, when a fan-in-fan-out device is used, the influence of crosstalk in the device can be suppressed, and the crosstalk can be determined more accurately.

[0020] A seventh aspect of the present invention is the crosstalk measurement method according to any one of the first to sixth aspects, wherein the optical device further comprises a third optical waveguide arranged in parallel with the first optical waveguide, and the processing step further determines the magnitude of crosstalk between the first optical waveguide and the third optical waveguide based on the determined magnitude of crosstalk between the first optical waveguide and the second optical waveguide.

[0021] In this case, the magnitude of the crosstalk between the first optical waveguide and the third optical waveguide can be easily obtained without measuring the optical power due to the crosstalk between the first optical waveguide and the third optical waveguide. Note that in this case, the magnitude of the crosstalk between the first optical waveguide and the third optical waveguide is obtained, for example, using a relational expression that shows the relationship between the magnitude of the crosstalk between the first optical waveguide and the second optical waveguide and the magnitude of the crosstalk between the first optical waveguide and the third optical waveguide.

[0022] In an eighth aspect of the present invention, the optical device further includes a third optical waveguide arranged in parallel with the first optical waveguide, and in the connecting step, the other end of the first optical waveguide and the other end of the third optical waveguide are optically connected via a second connecting optical waveguide having a length different from that of the first connecting optical waveguide, and in the first measuring step, a crosstalk of the incident light from the first optical waveguide to the third optical waveguide and a crosstalk of the incident light from the first optical waveguide to the third optical waveguide are measured. and light generated by crosstalk from the third optical waveguide to the first optical waveguide, and a power of the output light output from the one end of the first optical waveguide is further measured by the OTDR, and in the processing step, a magnitude of the crosstalk between the first optical waveguide and the third optical waveguide is further determined using the power of the output light including the pulsed light generated by crosstalk between the first optical waveguide and the third optical waveguide.

[0023] In this case, as described in Aspect 1, crosstalk occurs between the first optical waveguide and the second optical waveguide, and output light including pulsed light due to the crosstalk is output from one end of the first optical waveguide. Furthermore, in this aspect, crosstalk occurs between the first optical waveguide and the third optical waveguide, and output light including pulsed light due to the crosstalk is output from one end of the first optical waveguide. At this time, since the first connecting optical waveguide and the second connecting optical waveguide have different lengths, pulsed light due to crosstalk between the first optical waveguide and the second optical waveguide and pulsed light due to crosstalk between the first optical waveguide and the third optical waveguide are output from one end of the first optical waveguide at different times. Therefore, by receiving the output light containing pulsed light due to crosstalk between the first optical waveguide and the second optical waveguide and the output light containing pulsed light due to crosstalk between the first optical waveguide and the third optical waveguide with an OTDR, the power of each output light can be measured, and the magnitude of each crosstalk can be determined. Therefore, compared to the case in which the crosstalk between the first optical waveguide and the second optical waveguide is measured, and then the first optical waveguide and the third optical waveguide are optically connected by a connecting optical waveguide and incident light is again introduced from one end of the first optical waveguide to measure the crosstalk between the first optical waveguide and the third optical waveguide, as in Aspect 1, the crosstalk between the first optical waveguide and the second optical waveguide and the crosstalk between the first optical waveguide and the third optical waveguide can each be easily measured.

[0024] In the eighth aspect, it is preferable that the difference between the length of the first connection optical waveguide and the length of the second connection optical waveguide is larger than the half-width of the incident light.

[0025] In this case, interference between the pulsed light due to crosstalk between the first optical waveguide and the second optical waveguide and the pulsed light due to crosstalk between the first optical waveguide and the third optical waveguide can be suppressed, and the magnitude of the crosstalk can be measured more accurately.

[0026] In a ninth aspect of the present invention, the optical device further includes a third optical waveguide arranged in parallel with the second optical waveguide, and the connecting step further includes optically connecting one end of the second optical waveguide to one end of the third optical waveguide via a second connecting optical waveguide, and the first measuring step further includes measuring light generated by crosstalk from the second optical waveguide to the third optical waveguide caused by the incident light incident from the first optical waveguide to the second optical waveguide via the first connecting optical waveguide and light generated by crosstalk from the second optical waveguide to the third optical waveguide caused by the incident light incident from the second optical waveguide to the third optical waveguide via the second connecting optical waveguide. and a power of the output light emitted from the one end of the first optical waveguide via the first connecting optical waveguide and the first optical waveguide, the output light including pulsed light generated by crosstalk from the second optical waveguide to the third optical waveguide, is further measured by the OTDR, and in the processing step, the magnitude of the crosstalk between the second optical waveguide and the third optical waveguide is further determined using the power of the output light including pulsed light generated by crosstalk between the second optical waveguide and the third optical waveguide.

[0027] In this case, as described in Aspect 1, crosstalk occurs between the first optical waveguide and the second optical waveguide, and output light containing pulsed light due to the crosstalk is output from one end of the first optical waveguide. Furthermore, in this aspect, pulsed incident light entering the second optical waveguide from the other end of the second optical waveguide via the first optical waveguide and the first connecting optical waveguide propagates from the second optical waveguide to the third optical waveguide while crosstalking. Therefore, crosstalk light crosstalking from the second optical waveguide to the third optical waveguide also becomes pulsed and propagates from the other end to one end of the third optical waveguide while traveling generally parallel to the incident light. Incident light reaching one end of the second optical waveguide enters the second connecting optical waveguide. Furthermore, crosstalk light reaching one end of the third optical waveguide enters the second connecting optical waveguide from the opposite side to the incident light. As described above, since the propagation velocities of the incident light and the crosstalk light are equal, the incident light and the crosstalk light, which arrive at one end at approximately the same time, intersect at approximately the midpoint of the second connecting optical waveguide. The incident light enters the third optical waveguide from one end, and the crosstalk light enters the second optical waveguide from one end. At this time, the timing at which the incident light enters the third optical waveguide and the timing at which the crosstalk light enters the second optical waveguide are approximately the same. Therefore, the crosstalk light propagates from one end to the other end of the second optical waveguide while traveling approximately parallel to the incident light propagating from one end to the other end of the third optical waveguide. During this time, the incident light propagating through the third optical waveguide propagates while crosstalking with the second optical waveguide. Therefore, light that crosstalks from the third optical waveguide to the second optical waveguide is combined with the crosstalk light propagating through the second waveguide. The combined light is pulsed, and the outgoing light that passes through the first connecting optical waveguide and the first optical waveguide and is output from one end of the first optical waveguide contains pulsed light generated by the crosstalk between the second optical waveguide and the third optical waveguide. The outgoing light that exits the first optical waveguide is received by an OTDR, and the power of the outgoing light is measured.

[0028] At this time, pulsed light due to crosstalk between the first optical waveguide and the second optical waveguide and pulsed light due to crosstalk between the second optical waveguide and the third optical waveguide are emitted from one end of the first optical waveguide at different times. Therefore, the emitted light including the light due to crosstalk between the first optical waveguide and the second optical waveguide and the emitted light including the light due to crosstalk between the second optical waveguide and the third optical waveguide are received by the OTDR, and the power of each emitted light can be measured, thereby determining the magnitude of each crosstalk. Therefore, compared to the case in which, after measuring the crosstalk between the first optical waveguide and the second optical waveguide as in aspect 1, the other end of the second optical waveguide and the other end of the third optical waveguide are optically connected by a connecting optical waveguide, and incident light is again made incident from one end of the second optical waveguide to measure the crosstalk between the second optical waveguide and the third optical waveguide, it is possible to easily measure the crosstalk between the first optical waveguide and the second optical waveguide and the crosstalk between the second optical waveguide and the third optical waveguide.

[0029] In a tenth aspect of the present invention, the optical device further includes a third optical waveguide arranged in parallel with the first optical waveguide, and the connecting step further optically connects one end of the second optical waveguide and the other end of the third optical waveguide via a second connecting optical waveguide, and the first measuring step further comprises measuring light generated by crosstalk of the incident light incident from the OTDR into the first optical waveguide from the first optical waveguide to the third optical waveguide, and measuring the light from the first optical waveguide to the third optical waveguide via the first connecting optical waveguide, the second optical waveguide, and the second connecting optical waveguide. The crosstalk measurement method according to any one of Aspects 1, 2, 5, and 6, is characterized in that the incident light includes pulsed light generated by combining the incident light with light generated by crosstalk from the third optical waveguide to the first optical waveguide, the power of the outgoing light output from the one end of the first optical waveguide is further measured by the OTDR, and in the processing step, the magnitude of the crosstalk between the first optical waveguide and the third optical waveguide is further determined using the power of the outgoing light including pulsed light generated by crosstalk between the first optical waveguide and the third optical waveguide.

[0030] In this case, as described in Aspect 1, crosstalk occurs between the first optical waveguide and the second optical waveguide, and output light containing pulsed light due to the crosstalk is output from one end of the first optical waveguide. Furthermore, in this aspect, incident light propagating through the first optical waveguide propagates from the first optical waveguide to the third optical waveguide while crosstalking, and the crosstalk light crosstalking from the first optical waveguide to the third optical waveguide also becomes pulsed and propagates from one end to the other end of the third optical waveguide while traveling generally parallel to the incident light propagating through the first optical waveguide. The incident light reaching the other end of the first optical waveguide is incident on the first connecting optical waveguide. The crosstalk light reaching the other end of the third optical waveguide is incident on the second connecting optical waveguide. As described above, since the propagation velocities of the incident light and the crosstalk light are equal, the incident light and the crosstalk light intersect approximately at the midpoint of the optical waveguide formed by combining the first connecting optical waveguide, the second optical waveguide, and the second connecting optical waveguide. The incident light enters the third optical waveguide from the other end of the third optical waveguide via the second connecting optical waveguide, and the crosstalk light enters the first optical waveguide from the other end of the first optical waveguide via the first connecting optical waveguide. At this time, the timing at which the incident light enters the third optical waveguide and the timing at which the crosstalk light enters the first optical waveguide are approximately the same. Therefore, the crosstalk light propagates from the other end to one end of the first optical waveguide while traveling approximately parallel to the incident light propagating from the other end to one end of the third optical waveguide. During this time, the incident light propagating through the third optical waveguide propagates while crosstalking into the first optical waveguide. Therefore, the light that crosstalks from the third optical waveguide to the first optical waveguide is combined with the crosstalk light propagating through the first optical waveguide. The combined light is pulsed, and the output light that is output from one end of the first optical waveguide contains pulsed light generated by the crosstalk between the first optical waveguide and the third optical waveguide. The light that is output from the first optical waveguide is received by an OTDR, and the power of this output light is measured.

[0031] At this time, pulsed light due to crosstalk between the first optical waveguide and the second optical waveguide and pulsed light due to crosstalk between the first optical waveguide and the third optical waveguide are emitted from one end of the first optical waveguide at different times. Therefore, the emitted light including the light due to crosstalk between the first optical waveguide and the second optical waveguide and the emitted light including the light due to crosstalk between the first optical waveguide and the third optical waveguide are each received by an OTDR, and the power of each emitted light can be measured, thereby determining the magnitude of each crosstalk. Therefore, compared to the case in which, after measuring the crosstalk between the first optical waveguide and the second optical waveguide as in aspect 1, the other end of the first optical waveguide and the other end of the third optical waveguide are optically connected by a connecting optical waveguide, and incident light is again made incident from one end of the first optical waveguide to measure the crosstalk between the first optical waveguide and the third optical waveguide, it is possible to easily measure the crosstalk between the first optical waveguide and the second optical waveguide and the crosstalk between the first optical waveguide and the third optical waveguide.

[0032] Aspect 11 of the present invention is the crosstalk measurement method according to any one of Aspects 1 to 10, characterized in that in the first measurement step, the OTDR further measures at least one of optical loss, reflection intensity, bending loss, and open circuit in the optical device.

[0033] In this case, the above measurements can be performed in parallel with the crosstalk measurement, thereby reducing the effort required for measurements other than crosstalk.

[0034] A twelfth aspect of the present invention is the crosstalk measurement method according to any one of Aspects 1 to 11, characterized in that when light of the same power is propagated through the first optical waveguide, the second optical waveguide, and the first connecting optical waveguide, the power of backscattered light per unit length generated in the first connecting optical waveguide is smaller than the power of backscattered light per unit length generated in each of the first optical waveguide and the second optical waveguide.

[0035] In the first connection optical waveguide, the power of the backscattered light is small, so that the ratio of the power of the crosstalk light to the power of the backscattered light is large, making it easier to detect the crosstalk light.

[0036] A thirteenth aspect of the present invention is a crosstalk measurement apparatus for an optical device having a first optical waveguide and a second optical waveguide which are arranged in parallel and include one end and the other end, the crosstalk measurement apparatus comprising: a first connecting optical waveguide which optically connects the other end of the first optical waveguide and the other end of the second optical waveguide; an OTDR which makes pulsed incident light incident on the one end of the first optical waveguide, the OTDR including pulsed light which is generated by crosstalk of the incident light from the first optical waveguide to the second optical waveguide, and light which is generated by crosstalk of the incident light which enters the second optical waveguide from the first optical waveguide via the first connecting optical waveguide to the first optical waveguide, the OTDR measuring the power of output light which exits from the one end of the first optical waveguide; and a processing unit which calculates the magnitude of crosstalk between the first optical waveguide and the second optical waveguide using the measured power of the output light.

[0037] According to the crosstalk measurement device of this aspect, the OTDR is used to measure light that crosstalks into other optical waveguides, and therefore the power of the crosstalk light is greater than when detecting backscattered light from the crosstalked light as in Patent Documents 2 and 3. Furthermore, in the crosstalk measurement device of this aspect, the crosstalk light generated when the incident light propagates from one end of the first optical waveguide to the other end and the crosstalk light generated when the incident light propagates from the other end of the second optical waveguide to one end are combined, so the power of the pulsed light generated by the crosstalk tends to be greater. Therefore, the crosstalk measurement device of this aspect can easily measure crosstalk.

[0038] As described above, the present invention provides a crosstalk measurement method and a crosstalk measurement device that can easily measure crosstalk using the OTDR method.

[0039] 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 according to the first embodiment. FIG. 7 is a flowchart showing the procedure of a crosstalk measurement method according to 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. 3. FIG. 9 is a diagram showing measurement results by an OTDR. FIG. 10 is an enlarged view of a part of FIG. 10. FIG. 11 is a diagram showing the power of crosstalk light measured by an OTDR when the length of a multi-core fiber is changed. FIG. 12 is a diagram showing the relationship between the power of crosstalk light measured in the first embodiment and the power of crosstalk light measured by the PM method. FIG. 13 is a flowchart showing the procedure of a crosstalk measurement method according to a second embodiment of the present invention. FIG. 14 is a diagram showing the state of the crosstalk measurement device in a second measurement step of the second embodiment. FIG. 15 is a diagram showing a crosstalk measurement device according to a third embodiment of the present invention. FIG. 16 is a diagram showing measurement results by an OTDR in the third embodiment. FIG. 17 is a diagram showing a crosstalk measurement device according to a fourth embodiment of the present invention. FIG. 18 is a diagram showing a crosstalk measurement device according to a fifth embodiment of the present invention. FIG. 19 is a diagram showing measurement results by an OTDR when a hollow-core optical fiber is used as the first optical fiber in FIG. 4. FIG. 19 is a diagram showing a modification of the crosstalk measurement device of the first embodiment.

[0040] 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 thereof. Note that in the drawings referred to below, the dimensions of each component may be changed to facilitate understanding.

[0041] 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.

[0042] 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 can be considered as a first optical waveguide to a fourth optical waveguide, and the multicore fiber 10 is an optical device having a plurality of optical waveguides arranged in parallel with one another.

[0043] 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.

[0044] 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, and a first optical fiber 51, 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.

[0045] The OTDR 20 is used by being connected to an optical fiber or the like, and is an instrument that can emit pulsed light, measure the power of light incident from the multicore fiber 10, and measure the time from when the pulsed light is emitted until the measured light is incident, and can measure light losses such as transmission loss, bending loss, connection loss, etc. of optical fibers, detect breaks in optical fibers, etc., measure the amount of light reflection, etc. In this embodiment, a fan-in-fan-out device 30 is connected to the OTDR 20.

[0046] 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 core of the optical fiber 31 is connected to the OTDR 20. Also, in this example, the optical waveguide connected to the core of the optical fiber 31 is connected to the core 11 of the multicore fiber 10. Therefore, the optical fiber 31 and the core 11 are optically connected, and light output from the OTDR 20 is incident on the core 11.

[0047] 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 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 core 11 is optically connected to the core of the optical fiber 41, and the core 12 is optically connected to the core of the optical fiber 42.

[0048] The first optical fiber 51 is a single-core fiber, for example a single-mode fiber. The optical fiber 41 is connected to one end of the first optical fiber 51, and the optical fiber 42 is connected to the other end of the first optical fiber 51. Therefore, the core of the optical fiber 41 and the core of the optical fiber 42 are optically connected via the core of the first optical fiber 51. The core of the first optical fiber 51 can be considered as a first connecting waveguide that optically connects the other end of the first optical waveguide, which is the core 11, and the other end of the second optical waveguide, which is the core 12.

[0049] 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 the magnitude of 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 processing unit 25 receives the data related to the power of light from the OTDR 20, the processing unit 25 calculates the magnitude of crosstalk between the core 11 and the core 12 based on the data, as described below, and outputs data related to the calculated magnitude of crosstalk. The processing unit 25 and the OTDR 20 may be housed in a single housing, and some components may be shared.

[0050] 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 connection step S1, a first measurement step S2, and a processing step S3.

[0051] (Connection Step S1) Prior to this step, a multicore fiber 10 is prepared as the optical device under test and set in the crosstalk measurement apparatus 1. The length of the multicore fiber 10 is, for example, 21 km. At this time, in this step, the other end 18 of the core 11 and the other end 18 of the core 12 are optically connected via the core of the first optical fiber 51. The length of the first optical fiber 51 is, for example, 10 km. Specifically, the waveguide connected to the optical fiber 41 in the fan-in-fan-out device 40 is connected to the core 11 of the multicore fiber 10, and the waveguide connected to the optical fiber 42 is connected to the core 12. Therefore, in this step, the other end of the first optical waveguide and the other end of the second optical waveguide are optically connected via the first connecting optical waveguide. After this step, when light is incident from one end 17 of the core 11, the light is incident on the core 12 from the other end 18 of the core 12 via the core of the first optical fiber 51.

[0052] The OTDR 20 is also optically connected to the core 11. Specifically, a waveguide connected to the optical fiber 31 in the fan-in-fan-out device 30 is connected to the core 11 of the multicore fiber 10. Therefore, light emitted from the OTDR 20 enters the core 11 from one end 17 of the core 11.

[0053] In this way, the core 11 of the multicore fiber 10 and the OTDR 20 are optically connected, and the core 11 and the core 12 are optically connected via the core of the first optical fiber 51, as shown in Figure 2.

[0054] (First measurement step S2) In this step, pulsed incident light output from the OTDR 20 is input from one end 17 of the core 11, which is the first optical waveguide, and the power of the output light output from one end 17 of the core 11 is measured by the OTDR 20, and includes pulsed light that is a combination of light generated when the incident light crosstalks from the core 11 to the core 12, which is the second optical waveguide, and light generated when the incident light that enters from the core 11 to the core 12 via the core of the first optical fiber 51, which is the first connecting optical waveguide, crosstalks from the core 12 to the core 11.

[0055] FIG. 4 is a diagram showing the propagation of light in the crosstalk measurement device of FIG. 3. 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 form in FIG. 3. 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 below, 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 in pulse width so that the emitted light, including the crosstalk light described below, does not become saturated. In this case, an attenuator may be interposed between the OTDR 20 and the optical fiber 31.

[0056] 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 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.

[0057] Next, the incident light L and the crosstalk light CL1 are incident on the core of the first optical fiber 51 at approximately the same time via the fan-in-fan-out device 40. At this time, the crosstalk light CL1 is incident on the side opposite to the side on which the incident light L is incident on the core of the first optical fiber 51. The incident light L and the crosstalk light CL1 incident on the core of the first optical fiber 51 intersect at approximately the midpoint of the first optical fiber 51. The incident light L and the crosstalk light CL1 reach different ends of the first optical fiber 51 at approximately the same time. 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, respectively, at approximately the same time. Even if the optical fibers 41 and 43 in the fan-in-fan-out device 40 have different lengths, the incident light L and the crosstalk light CL1 enter the cores 12 and 11, respectively, at approximately the same time.

[0058] 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.

[0059] 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.

[0060] FIG. 5 is a diagram showing the measurement results of the outgoing 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 outgoing light received by the OTDR 20. Note that the vertical axis of FIG. 5 represents the power of the outgoing 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 unit of the vertical axis may be dBm. As shown in FIG. 5, backscattered light is measured as the outgoing 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 lines representing the outgoing 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 core 11 and the section of first optical fiber 51, and at the boundary between the section of first optical fiber 51 and the section of core 12, and this light indicates reflection in the fan-in-fan-out device 40, etc.

[0061] Pulsed light is measured approximately at the midpoint of the section representing the first optical fiber 51. As described above, the incident light L and the crosstalk light CL1 intersect approximately at the midpoint of the first optical fiber 51, and therefore this pulsed light represents the crosstalk light CL1. Furthermore, backscattered light is also measured as emitted light in the section where the incident light L propagates through the first optical fiber 51. Therefore, the power of the emitted light measured approximately at the midpoint of the first optical fiber 51 includes the power of the crosstalk light CL1 and the power of the backscattered light.

[0062] As described above, a pulse indicating the power of the crosstalk light CL1 is shown at approximately the midpoint of the section indicating the first optical fiber 51. 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 overlapping the end of the first optical fiber 51, it is preferable that the core length of the first optical fiber 51, which is the first connecting optical waveguide, is longer than the half-width of the incident light L. In other words, the length of the first optical fiber 51 is set to L. SCF and the half-value time width of the incident light L is ΔT pulse When the refractive index of the core of the first optical fiber 51 is n and the high speed is c, it is preferable that the following formula be satisfied: LSCF >ΔT pulse ×c / n

[0063] It is more preferable to satisfy the following formula in order to further suppress the influence of the end of the first optical fiber 51 on the pulse: L SCF >1.2 x ΔT pulse ×c / n

[0064] The OTDR 20 outputs data relating to the measured power of the emitted light to the processing unit 25 .

[0065] (Processing Step S3) In this step, the magnitude of crosstalk between the cores 11 and 12 is determined using the power of the measured output light. Fig. 6 is an enlarged view of the output light measured approximately at the midpoint of the first optical fiber 51 in Fig. 5. As described above, backscattered light is also generated in the first optical fiber 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 output 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 in the fan-in-fan-out devices 30 and 40 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_MCFThis will give a more accurate power P XT_MCF This is preferable from the viewpoint of obtaining the above.

[0066] 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 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 first measurement step S2 described above, the power P of the pulsed light measured at approximately the midpoint of the first optical fiber 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.

[0067] The processing unit 25 calculates the power P of the crosstalk light CL1. XT_MCF The processing unit 25 converts the magnitude of the crosstalk into a decibel value that indicates the ratio of the power of the incident light L emitted from one end 17 of the core 12 and outputs the converted value. Alternatively, the processing unit 25 may convert the magnitude of the crosstalk into a decibel value that indicates the ratio to a predetermined power determined in the OTDR 20 shown in FIGS. 5 and 6 and output the converted value. In this way, the magnitude of the crosstalk is determined.

[0068] In this step, the processing unit 25 may further determine, for example, the magnitude of crosstalk between the core 11 and the core 13 based on the determined magnitude of crosstalk between the core 11 and the core 12. In this case, the processing unit 25 determines the magnitude of crosstalk between the core 11 and the core 13 based on the magnitude of crosstalk between the core 11 and the core 12, for example, by using a relational expression showing the relationship between the magnitude of crosstalk between the core 11 and the core 12 and the magnitude of crosstalk between the core 11 and the core 13. In this case, since the multicore fiber 10 which is an optical device has the core 13 which is a third optical waveguide which is arranged in parallel with the core 11 which is the first optical waveguide, in processing step S3, the magnitude of crosstalk between the first waveguide and the third waveguide is further determined based on the determined magnitude of crosstalk between the first waveguide and the second waveguide. In this case, the magnitude of crosstalk between the core 11 and the core 13 can be easily determined without measuring the power of light due to the crosstalk between the core 11 and the core 13. The magnitude of crosstalk between core 11 and core 14 may be calculated in the same manner as the magnitude of crosstalk between core 11 and core 13 .

[0069] Next, the reliability of the crosstalk measurement in this embodiment will be described.

[0070] 7 is a diagram showing the power of pulsed light composed of the crosstalk light CL1 in the multicore fiber 10 and the crosstalk light in the fan-in-fan-out devices 30 and 40 measured by the OTDR 20, similarly to the above embodiment, and the power of backscattered light is excluded from the power of light incident on the OTDR 20. As shown in FIG. 7, in this example, the length of the multicore fiber 10 is set to 0 km, 21 km, 42 km, and 84 km. The FIFO shown by the dotted line in FIG. 7 indicates that the fan-in-fan-out device 30 and the fan-in-fan-out device 40 are directly connected and the length of the multicore fiber 10 is 0 km, and the above power P XT_FIFO As shown in Fig. 7, it can be seen that the longer the multi-core fiber 10 is, the greater the power of light generated by crosstalk becomes.

[0071] Next, fan-in-fan-out devices 30 and 40 were connected to each of the multicore fibers 10 used in the measurement of Figure 7, and the magnitude of crosstalk was measured by the PM method. Specifically, light was incident on the core of the optical fiber 31 of the fan-in-fan-out device 30, which is optically connected to the core 11 of the multicore fiber 10, and the light emitted from the cores of the optical fibers 41 and 42 of the fan-in-fan-out device 40, which is optically connected to the core 12 of the multicore fiber 10, was measured, thereby measuring the magnitude of crosstalk between the core 11 and the core 12. Therefore, the magnitude of this crosstalk is the ratio of the power of the crosstalk light to the power of the incident light L emitted from one end 17 of the core 12. The results are shown in Table 1 below.

[0072] In Table 1, Peak Size is the power of the pulsed light shown in FIG. 7, and Crosstalk is the magnitude of the crosstalk measured by the PM method. FIG. 8 is a diagram showing the relationship between the power of the crosstalk light measured in this embodiment and the power of the crosstalk light measured by the PM method, as shown in Table 1. As shown in FIG. 8, these relationships are linear. Therefore, it was shown that the power of the crosstalk light measured by the crosstalk measurement method of this embodiment is roughly correlated with the magnitude of the crosstalk measured by the PM method. When each point shown in FIG. 8 is approximated by a straight line, the straight line is expressed by the following equation: XT=2.57x-58.9R ２ = 0.986 where XT represents the magnitude of crosstalk, x represents the power of crosstalk light, and R ２ is the coefficient of determination. As shown, the coefficient of determination is very close to 1, which indicates that the correlation is high.

[0073] Next, a plurality of other multi-core fibers 10 were prepared, and the magnitude of crosstalk was measured in the same manner as in this embodiment. At this time, the power of the pulsed crosstalk light was measured in the same manner as in the first measurement step S2, and the magnitude of this power was substituted for x in the above equation to determine the magnitude of crosstalk shown in decibels on the vertical axis of Fig. 8. In addition, the crosstalk of each multi-core fiber 10 was measured by the PM method. The results are shown in Table 2.

[0074] In Table 2, XT calculation is the magnitude of crosstalk calculated using the above linear approximation formula, and XT measurement is the magnitude of crosstalk measured by the PM method. As shown in Table 2, the results of the crosstalk measurement according to this embodiment and the results of the crosstalk measurement by the PM method generally matched. Therefore, in processing step S3, when the processing unit 25 converts the magnitude of crosstalk into decibels indicating the ratio of the power of the incident light L output from one end 17 of the core 12, the power of the pulsed crosstalk light may be defined as x and the magnitude of crosstalk XT may be calculated from the above linear approximation formula.

[0075] From the above, it has been shown that the crosstalk measurement of this embodiment is reliable.

[0076] Next, the measurement of crosstalk in this embodiment will be explained using mathematical expressions.

[0077] The length of the multi-core fiber 10 is L MCF and the length of the first optical fiber 51 is L SCF Furthermore, the power of the incident light L when it enters the core 11 of the multi-core fiber 10 from one end 17 is P ０ The power of the incident light L when it is emitted from the other end 18 is P'. ０ The power of the incident light L when it enters the core 12 from the other end 18 and exits from the one end 17 of the core 12 is P" ０ Furthermore, the power of crosstalk light that crosstalks from the core 11 to the core 12 while the incident light L propagates through the core 11 and is emitted from the core 12 is P XT (L MCF), and while the incident light L propagates through the core 11 and the core 12, that is, while the incident light L travels back and forth through the multi-core fiber 10, the power P of the crosstalk light that crosstalks between the core 11 and the core 12 and is emitted from the core 11 is XT (2L MCF )

[0078] For simplicity, in the following explanation using the mathematical formulas, the multicore fiber 10 will be described as a two-core fiber that has cores 11 and 12 but does not have cores 13 and 14. Furthermore, the transmission loss of the multicore fiber 10 and the first optical fiber 51 will be ignored, and the loss and crosstalk in the fan-in-fan-out devices 30 and 40 will also be ignored. In this case, referring to formulas (21a) and 21(b) in Non-Patent Document 1, P' ０ , P” ０ , P XT (L MCF ), P XT (2L MCF ) are represented by the following formulas (1) to (4).

[0079] In the above formula, h is the power coupling coefficient between the crosstalking cores 11 and 12. The unit of optical power here is not expressed in decibels but is expressed in watts, for example.

[0080] Furthermore, the magnitude of crosstalk from the core 11 to the core 12 while the incident light L is propagating through the core 11 is denoted by P'. ０ The magnitude expressed in decibels as a ratio to XT(L MCF ), and while the incident light L propagates through the cores 11 and 12, that is, while the incident light L travels back and forth through the multi-core fiber 10, the magnitude of crosstalk between the cores 11 and 12 is defined as P″ ０ The magnitude expressed in decibels as a ratio to XT(2L MCF ) In this case, XT(L MCF ), XT (2L) MCF ) are expressed by the following formulas (5) and (6).

[0081] As described above, the OTDR 20 is optically connected to the core 11 at one end 17 of the multi-core fiber 10. Therefore, in the OTDR, P" ０ Therefore, the XT (2L) is calculated from the optical power measured by the OTDR 20. MCF ) can be obtained using equation (6) as follows:

[0082] As described above, the incident light L and the crosstalk light CL1 intersect at approximately the midpoint of the first optical fiber 51. At this time, the propagation distance of the incident light L is the length L of the multi-core fiber 10. MCF and half the length L of the first optical fiber 51 SCF Therefore, the distance from the midpoint of the first optical fiber 51 to the one end 17 of the multi-core fiber 10 is L MCF +L SCF The intensity of the backscattered light from the midpoint of the first optical fiber 51 measured by the OTDR 20 is P BS (L MCF +L SCF / 2), then P BS (L MCF +L SCF / 2) is shown in equation (7)

[0083] In formula (7), α Ｓ_SCF is the backscattering coefficient of the first optical fiber 51 and represents the probability that the incident light L undergoes Rayleigh scattering in the first optical fiber 51, and B SCF indicates the probability that the light Rayleigh scattered at the capture rate of the first optical fiber 51 propagates through the core of the first optical fiber 51 toward the core 11 of the multi-core fiber 10.

[0084] Equation (8) is derived from equations (2) and (7).

[0085] From equation (8), P ０ is calculated and substituted into equation (6), equation (9) is obtained.

[0086] As explained in processing step S3, P BS (L MCF +L SCF / 2) can be obtained from the power of the emitted light in the region other than the region where the pulsed crosstalk light is shown, based on the data input from the OTDR 20. In this description, crosstalk in the fan-in-fan-out devices 30 and 40 is ignored, so the power P XT_MCF P XT (2L MCF ) Therefore, P XT (2L MCF ) can be obtained as explained in the processing step S3. Therefore, by separately calculating the first term of the formula (9), XT(2L MCF The first term of the formula (9) is calculated by the magnitude of the crosstalk calculated in advance by the PM method and the P measured by the OTDR 20. BS (L MCF +L SCF / 2) and P XT (2L MCF ) or the first term of equation (9) may be obtained by measuring the first optical fiber 51 in advance.

[0087] As described above, the crosstalk measurement method of this embodiment includes a connecting step S1 of optically connecting the other end 18 of the core 11, which is the first optical waveguide, and the other end 18 of the core 12, which is the second optical waveguide, via the core of the first optical fiber 51, which is the first connecting optical waveguide; a first measuring step S2 of measuring, by the OTDR 20, the power of the output light output from the one end 17 of the core 11, which includes pulsed crosstalk light CL1 that is a combination of light generated when the incident light L crosstalks from the core 11 to the core 12 and light generated when the incident light L enters the core 11 from the core 12 via the core of the first optical fiber 51 and crosstalks from the core 12 to the core 11; and a processing step S3 of calculating the magnitude of the crosstalk between the core 11 and the core 12 using the power of the output light that has been measured.

[0088] The crosstalk measuring device of this embodiment also includes a core of a first optical fiber 51 that optically connects the other end 18 of the core 11 and the other end 18 of the core 12, an OTDR 20 that measures the power of the outgoing light that is emitted from one end 17 of the core 11, and that includes pulsed crosstalk light CL1 that is a combination of light generated when pulsed incident light L is incident from one end 17 of the core 11 and the incident light L crosstalks from core 11 to core 12, and light generated when the incident light L that is incident from core 11 to core 12 via the core of the first optical fiber 51 crosstalks from core 12 to core 11, and a processing unit 25 that uses the power of the measured outgoing light to determine the magnitude of crosstalk between the cores 11 and 12.

[0089] According to this crosstalk measurement method and crosstalk measurement device, the OTDR 20 is used to detect light that crosstalks from light incident on the core 11 to the core 12, and therefore the power of the crosstalk light is greater than when detecting backscattered light from the crosstalked light as in Patent Documents 2 and 3. Furthermore, in the crosstalk measurement method and crosstalk measurement device of this embodiment, light that crosstalks when the incident light L propagates from one end 17 to the other end 18 of the core 11 and light that crosstalks when the incident light L propagates from the other end 18 to one end 17 of the core 12 are combined, and therefore the power of the pulsed crosstalk light CL1 generated by crosstalk tends to be greater. Therefore, according to the crosstalk measurement method and crosstalk measurement device of this aspect, crosstalk can be easily measured.

[0090] Second Embodiment Next, a second embodiment of the present invention will be described in detail with reference to Figures 9 and 10. Note that components that are the same as or equivalent to those in the above embodiment will be given the same reference numerals and redundant description will be omitted unless otherwise specified.

[0091] 9 is a flowchart showing the steps of the crosstalk measurement method of this embodiment. As shown in FIG. 9, the crosstalk measurement method of this embodiment differs from the crosstalk measurement method of the first embodiment in that it includes a second measurement step S22. In this embodiment, the connection step S1 and the first measurement step S2 are performed in the same manner as the crosstalk measurement method of the first embodiment.

[0092] (Second Measuring Step S22) In this embodiment, this step is performed after the first measuring step S2. Fig. 10 is a diagram showing the state of the crosstalk measuring device in this step. As shown in Fig. 10, in this step, the core of the optical fiber 32 of the fan-in-fan-out device 30 is connected to the OTDR 20. The optical waveguide connected to the core of the optical fiber 32 is connected to the core 12 of the multicore fiber 10. Therefore, the optical fiber 32 and the core 12 are optically connected, and light output from the OTDR 20 enters the core 12 from one end 17.

[0093] In this step, pulsed incident light output from the OTDR 20 is incident on one end 17 of the core 12, which is the second optical waveguide. In this case, a multi-channel OTDR may be used, and in the first measurement step S2, light may be incident on the core 11 from one channel of the OTDR 20, and in this step, light may be incident on the core 12 from the other channel of the OTDR 20. In this step, the power of the incident light L incident on the core 12 from the OTDR 20 is the same as the power of the incident light L incident on the core 12 from the OTDR 20 in the first measurement step S2. The incident light L incident on the core 12 crosstalks from the core 12 to the core 11, which is the first optical waveguide. The incident light L propagating to the other end 18 of the core 12 is incident on the core 11 from the core 12 via the core of the first optical fiber 51, which is the first connecting optical waveguide. Incident light L entering core 11 crosstalks from core 11 to core 12. Outgoing light including pulsed crosstalk light CL2 resulting from the combination of light generated by crosstalk from core 12 to core 11 and light generated by crosstalk from core 11 to core 12 is emitted from one end 17 of core 12.

[0094] The OTDR 20 measures the power of the emitted light. The power distribution of the emitted light measured in this step is approximately the same as the power of the emitted light measured in the first measurement step shown in Fig. 5. However, the description of core 11 and the description of core 12 in Fig. 5 should be read interchangeably.

[0095] (Processing Step S3) In processing step S3 of this embodiment, first, the processing unit 25 inverts the range from core 12 to core 11 of the optical power distribution measured in the second measurement step S22 along the horizontal axis. Then, the processing unit 25 takes the arithmetic mean of the optical power distribution in the range from core 11 to core 12 measured in the first measurement step S2 and the optical power distribution inverted in this step. 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 optical power distribution in the range of core 11 in FIG. 5 is substantially eliminated. Similarly, the gradient of the optical power distribution representing the range of core 12 in FIG. 5 and the gradient of the optical power distribution in the range of the first optical fiber 51 are substantially eliminated. Furthermore, at approximately the midpoint of the first optical fiber 51, a pulse of crosstalk light, which is an average of the crosstalk light CL1 and the crosstalk light CL2, appears.

[0096] Next, in this step, the processing unit 25 obtains the magnitude of the crosstalk light from the averaged power of the pulsed crosstalk light in the same manner as in the first embodiment.

[0097] As described above, in addition to the crosstalk measurement method of the first embodiment, the crosstalk measurement method of this embodiment includes a second measurement step S22 in which pulsed incident light L output from the OTDR 20 is input from one end 17 of the core 12, and the power of the output light output from one end 17 of the core 12 is measured by the OTDR 20, the pulsed light being a combination of light generated by crosstalk from the incident light L from the core 12 to the core 11 and light generated by crosstalk from the core 11 to the core 12 of the incident light L input from the core 12 to the core 11 via the core of the first optical fiber 51. In processing step S3, the power of the output light measured in the first measurement step S2 and the power of the output light measured in the second measurement step S22 are used to determine the magnitude of crosstalk between the core 11 and the core 12.

[0098] Furthermore, in the crosstalk measuring device of this embodiment, in addition to the crosstalk measuring device of the first embodiment, the OTDR 20 inputs pulsed incident light L from one end 17 of the core 12, and includes pulsed light that is a combination of light generated when the incident light L crosstalks from the core 12 to the core 11 and light generated when the incident light L that enters the core 11 from the core 12 via the core of the first optical fiber 51 crosstalks from the core 11 to the core 12, the OTDR 20 measures the power of the outgoing light that exits from the one end 17 of the core 12, and the processing unit 25 calculates the magnitude of crosstalk between the core 11 and the core 12 using the power of the outgoing light that exits from the one end 17 of the core 11 due to the incident light L that enters from the core 11, and the power of the outgoing light that exits from the one end 17 of the core 12 due to the incident light L that enters from the core 12.

[0099] According to the crosstalk measurement method and crosstalk measurement device of this embodiment, crosstalk light CL1 generated by propagating incident light L from core 11 to core 12 and crosstalk light CL2 generated by propagating incident light L from core 12 to core 11 are used, so the magnitude of crosstalk can be determined more accurately than when only crosstalk light CL1 generated by propagating incident light L from core 11 to core 12 is used.

[0100] Furthermore, the power of the incident light L incident on the core 11 in the first measurement step S2 and the power of the incident light L incident on the core 12 in the second measurement step S22 are equal to each other, and in processing step S3, the magnitude of crosstalk between the cores 11 and 12 is determined using the result of averaging the power of the output light measured in the first measurement step S2 and the power of the output light measured in the second measurement step S22. By using such averaging processing, the magnitude of crosstalk can be easily and accurately determined. Note that the power of the incident light L incident on the core 11 in the first measurement step S2 and the power of the incident light L incident on the core 12 in the second measurement step S22 may be different from each other. In this case, processing in processing step S3 is performed taking into account the power of the incident light L. For example, if the power of the incident light L incident on the core 12 in the second measurement step S22 is twice the power of the incident light L incident on the core 11 in the first measurement step S2, then in processing step S3, the power of the emitted light is halved and an averaging process is performed.

[0101] Third Embodiment Next, a third embodiment of the present invention will be described in detail with reference to Figures 11 and 12. Note that components that are the same as or equivalent to those in the above-described embodiments will be assigned the same reference numerals and redundant description will be omitted unless otherwise specified.

[0102] FIG. 11 is a diagram showing a crosstalk measurement device 1 according to this embodiment. The crosstalk measurement device 1 according to this embodiment differs from the crosstalk measurement device 1 according to the first embodiment in that an optical fiber 41 of a fan-in-fan-out device 40 is connected to one end of a first optical fiber 51 and a second optical fiber 52 via a coupler 55, and the other end of the second optical fiber 52 is connected to an optical fiber 43 of the fan-in-fan-out device 40. The optical waveguide connected to the core of the optical fiber 43 is connected to a core 13 of the multicore fiber 10, and the optical fiber 43 and the core 13 are optically connected. Therefore, the core of the first optical fiber 51 optically connects the cores 11 and 12, similar to the first optical fiber 51 according to the first embodiment, and the core of the second optical fiber 52 optically connects the cores 11 and 13. The core of the second optical fiber can be considered a second connecting waveguide. The length of the second optical fiber 52 is different from the length of the first optical fiber 51. In this embodiment, the second optical fiber 52 is described as being longer than the first optical fiber 51 .

[0103] Here, in this embodiment, the multicore fiber 10, which is an optical device, further has a third optical waveguide that is arranged in parallel with the first optical waveguide, which is the core 11. Moreover, the other end 18 of the first optical waveguide, which is the core 11, and the other end 18 of the third optical waveguide, which is the core 13, are optically connected via a second connecting optical waveguide having a length different from that of the first connecting optical waveguide.

[0104] The procedure of the crosstalk measurement method of this embodiment using such a crosstalk measurement device 1 is the same as that shown in the flowchart of Fig. 3. However, each step differs as follows. The differences will be mainly explained below.

[0105] (Connection Step S1) In this step of the present embodiment, the first optical fiber 51 and the second optical fiber 52 are connected to the optical fiber 41 via the coupler 55, and the end of the second optical fiber 52 opposite to the coupler 55 side is connected to the optical fiber 43. That is, in this embodiment, in addition to the connection step S1 in the first embodiment, the other end 18 of the core 11 and the other end 18 of the core 13 are optically connected via the core of the second optical fiber having a length different from that of the first optical fiber 51. In this way, the core 11 and the core 12 are optically connected, and the core 11 and the core 13 are optically connected.

[0106] (First measurement step S2) In this step of the present embodiment, as in the first embodiment, incident light L is incident on the core 11 from the OTDR 20. In this embodiment, in addition to the crosstalk between the core 11 and the core 12 described in the first embodiment, crosstalk occurs as follows, and this crosstalk is measured. This will be described below.

[0107] The incident light L entering the core 11 from the OTDR 20 propagates through the core 11 from one end 17 to the other end 18, crosstalking from the core 11 to the core 12 and also propagating from the core 11 to the core 13. The light crosstalking from the core 11 to the core 13 also takes the form of pulses, and propagates from one end 17 to the other end 18 of the core 13 while traveling generally parallel to the incident light L. The power of this crosstalk light CL2 increases according to the distance it propagates through the core 13. The crosstalk light CL2 enters the second optical fiber 52 from the optical fiber 43 at roughly the same time that the incident light L enters the second optical fiber 52 from the coupler 55. The incident light L and the crosstalk light CL2 intersect at roughly the midpoint of the second optical fiber 52. Then, via the fan-in-fan-out device 40, the incident light L enters the core 13 at the other end 18 of the multicore fiber 10, and the crosstalk light CL2 enters the core 11 at approximately the same timing as the incident light L enters the core 13. The incident light L that entered the core 13 and the crosstalk light CL2 that entered the core 11 propagate through the respective cores 13 and 11 toward one end 17 while traveling approximately parallel to each other. During this time, the incident light L propagating through the core 13 also propagates while crosstalking to the core 11. Therefore, the light that crosstalks from the core 13 to the core 11 is multiplexed with the crosstalk light CL2 propagating through the core 11. The multiplexed light is pulsed and propagates while gradually increasing in power. Outgoing light, in which the pulsed crosstalk light CL2 and light such as backscattered light are multiplexed, is emitted from one end 17 of the core 11. Therefore, the output light includes pulsed crosstalk light CL2. The output light 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.

[0108] 12 is a diagram showing measurement results of the OTDR in this embodiment. Because the lengths of the first optical fiber 51 and the second optical fiber 52 are different, as shown in FIG. 12 , the emitted light containing crosstalk light CL1 and the emitted light containing crosstalk light CL2 enter the OTDR 20 at different times. In this embodiment, because the second optical fiber 52 is longer than the first optical fiber 51, the emitted light containing crosstalk light CL2 enters the OTDR at a later time than the emitted light containing crosstalk light CL1. Therefore, the OTDR 20 can measure each of these emitted lights. Therefore, the OTDR 20 measures the power of the emitted light containing pulsed light twice.

[0109] It is preferable that the difference between the length of the first optical fiber 51 and the length of the second optical fiber 52 is larger than the half-width of the incident light. In this case, it is possible to suppress interference between the pulsed light due to crosstalk between the cores 11 and 12 and the pulsed light due to crosstalk between the cores 11 and 13, and it is possible to measure the magnitude of the crosstalk more accurately.

[0110] (Processing Step S3) In this step, the processing unit 25 uses the power of the measured output light to determine the magnitude of crosstalk between the cores 11 and 12 in the same manner as in the first embodiment. Furthermore, in this step of the present embodiment, the processing unit 25 determines the magnitude of crosstalk between the cores 11 and 13. Because backscattered light also occurs in the first optical fiber 51 and the second optical fiber 52, the power of this backscattered light is measured in areas other than the area where pulsed light including the crosstalk light CL2 is shown. Therefore, based on the data input from the OTDR 20, the processing unit 25 determines the power of the backscattered light in the area where pulsed light including the crosstalk light CL2 is shown from the power of the output light in areas other than the area where pulsed light including the crosstalk light CL2 is shown. Specifically, the processing unit 25 determines the power P of the backscattered light in the first embodiment. BSIn the same way as when the power of the crosstalk light CL2 in the fan-in-fan-out devices 30 and 40 was calculated, the power of the backscattered light in the output light including the crosstalk light CL2 is calculated. Next, the processing unit 25 calculates the difference between the power of the output light in the region where the pulsed light including the crosstalk light CL2 is shown and the power of the backscattered light calculated. This difference is the power of the crosstalk light CL2. In this embodiment as well, the crosstalk power P XT_FIFO However, if the power P XT_FIFO It is preferable to use the power obtained by removing the above as the power of the crosstalk light CL2 from the viewpoint of more accurately determining the power P of the crosstalk light CL2.

[0111] The processing unit 25 converts the power of the crosstalk light CL1 determined in the same manner as in the first embodiment into the magnitude of crosstalk and outputs the converted value, and also converts the power of the crosstalk light CL2 determined into the magnitude of crosstalk and outputs the converted value. At this time, the processing unit 25 may convert the magnitude of the crosstalk light CL2 into decibels indicating the ratio to the power of the incident light L emitted from one end 17 of the core 13 and output the converted value. The processing unit 25 may also convert the magnitude of the crosstalk light CL2 into decibels indicating the ratio to a predetermined power determined in the OTDR 20 and output the converted value. In this way, the magnitude of crosstalk between the core 11 and the core 12 and the magnitude of crosstalk between the core 11 and the core 13 are determined.

[0112] In the crosstalk measurement method of this embodiment, in addition to the crosstalk measurement method of the first embodiment, in the connection step S1, the other end 18 of the core 11 and the other end 18 of the core 13 are further optically connected via the core of a second optical fiber 52 having a length different from that of the core of the first optical fiber 51; in the first measurement step S2, the power of the output light output from one end 17 of the core 11 is further measured by the OTDR 20, which includes pulsed light that is a combination of light generated by crosstalk of the incident light L from the core 11 to the core 13 and light generated by crosstalk from the core 13 to the core 11 of the incident light L that enters the core 11 from the core 13 via the core of the second optical fiber 52; and in the processing step S3, the magnitude of the crosstalk between the core 11 and the core 13 is further determined using the power of the output light that includes pulsed crosstalk light CL2 generated by the crosstalk between the core 11 and the core 13.

[0113] In addition to the components of the crosstalk measurement device 1 of the first embodiment, the crosstalk measurement device 1 of this embodiment further includes a core of a second optical fiber 52 having a length different from that of the core of the first optical fiber 51 that optically connects the other end 18 of the core 11 and the other end 18 of the core 13, the OTDR 20 further measures the power of the output light emitted from one end 17 of the core 11, which includes pulsed light that is a combination of light generated by crosstalk of the incident light L from the core 11 to the core 13 and light generated by crosstalk from the core 13 to the core 11 when the incident light L enters the core 13 from the core 11 via the core of the second optical fiber 52, and the processing unit 25 further determines the magnitude of the crosstalk between the core 11 and the core 13 using the power of the output light that includes pulsed crosstalk light CL2 generated by the crosstalk between the core 11 and the core 13.

[0114] According to the crosstalk measurement method and crosstalk measurement device 1 of this embodiment, the output light including crosstalk light between core 11 and core 12 and the output light including crosstalk light between core 11 and core 13 are each received by OTDR 20, the power of each output light can be measured, and the magnitude of each crosstalk can be determined. Therefore, compared to the case in which the magnitude of crosstalk between core 11 and core 12 is measured as in the first embodiment, and then core 11 and core 13 are optically connected by a connecting optical waveguide and incident light is again made incident from one end 17 of core 11 to measure the magnitude of crosstalk between core 11 and core 13, the magnitude of crosstalk between core 11 and core 12 and the magnitude of crosstalk between core 11 and core 13 can each be easily measured.

[0115] In this embodiment, the second optical fiber 52 is described as being longer than the first optical fiber 51, but it is sufficient that the lengths of the first optical fiber 51 and the second optical fiber 52 are different, and the first optical fiber 51 may be longer than the second optical fiber 52.

[0116] Fourth Embodiment Next, a fourth embodiment of the present invention will be described in detail with reference to Fig. 13. Note that components that are the same as or equivalent to those in the above-described embodiments will be assigned the same reference numerals and redundant description will be omitted unless otherwise specified.

[0117] 13 is a diagram illustrating the crosstalk measurement device of this embodiment, following the example of FIG. 4. The crosstalk measurement device 1 of this embodiment differs from the crosstalk measurement device 1 of the first embodiment in that it includes a second optical fiber 52, and one end 17 of the core 12, which is the second optical waveguide, and one end of the core 13, which is the third optical waveguide, are optically connected via the core of the second optical fiber 52, which is the second connecting optical waveguide. In this embodiment, the lengths of the first optical fiber 51 and the second optical fiber 52 may be different from each other or may be the same.

[0118] The procedure of the crosstalk measurement method of this embodiment using such a crosstalk measurement device 1 is the same as that shown in the flowchart of Fig. 3. However, each step differs as follows. The differences will be mainly explained below.

[0119] (Connection Step S1) In this step of the present embodiment, in addition to the connection step S1 of the first embodiment, one end 17 of the core 12 and one end 17 of the core 13 are optically connected via the core of the second optical fiber 52. Specifically, one end of the second optical fiber 52 is connected to the optical fiber 32 of the fan-in-fan-out device 30, and the other end of the second optical fiber 52 is connected to the optical fiber 33 of the fan-in-fan-out device 30. In this way, the core 12 and the core 13 are optically connected.

[0120] (First measurement step S2) In this step of the present embodiment, as in the first embodiment, incident light L is incident on the core 11 from the OTDR 20. In this embodiment, in addition to the crosstalk between the core 11 and the core 12 described in the first embodiment, crosstalk occurs as follows, and this crosstalk is measured. This will be described below.

[0121] The incident light L entering the core 11 from the OTDR 20 propagates through the core 11 from one end 17 to the other end 18, and then enters the core 12 via the first optical fiber 51. The incident light L propagating through the core 12 from the other end 18 to the one end 17 crosstalks from the core 12 to the core 11, as described in the first embodiment, and also crosstalks from the core 12 to the core 13. The light crosstalking from the core 12 to the core 13 also becomes pulsed and propagates from the other end 18 of the core 13 to the one end 17 while traveling roughly parallel to the incident light L. The power of this crosstalk light CL2 increases according to the distance it propagates through the core 13. The incident light L enters the core 13 from the core 12 via the second optical fiber 52, and the crosstalk light CL2 enters the core 12 from the core 13 via the second optical fiber 52. The incident light L and the crosstalk light CL2 intersect at approximately the midpoint of the second optical fiber 52. Therefore, the timing at which the incident light L enters the core 13 and the timing at which the crosstalk light CL2 enters the core 12 are approximately the same. The incident light L that entered the core 13 and the crosstalk light CL2 that entered the core 12 propagate through the respective cores 13, 12 from one end 17 to the other end 18 while traveling approximately parallel to each other. During this time, the incident light L propagating through the core 13 also propagates while crosstalking with the core 12. Therefore, the light that crosstalks from the core 13 to the core 12 is multiplexed with the crosstalk light CL2 propagating through the core 12. The multiplexed light is pulsed and propagates while gradually increasing in power. The light including this pulsed crosstalk light CL2 enters the core 11 from the core 12 via the first optical fiber 51, and output light, in which the crosstalk light CL2 is combined with light such as backscattered light, is output from one end 17 of the core 11. Therefore, the output light includes the pulsed crosstalk light CL2. The output light from the core 11 enters the OTDR 20, is received by the OTDR 20, and its power is measured by the OTDR 20.

[0122] The timing at which the output light including the crosstalk light CL2 enters the OTDR 20 is delayed relative to the timing at which the output light including the crosstalk light CL1 enters the OTDR 20 by the time it takes for the light to propagate through the second optical fiber 52, the core 12, the first optical fiber 51, and the core 11. Therefore, the OTDR 20 can measure each of these output lights. Therefore, the OTDR 20 measures the power of the pulsed light twice.

[0123] (Processing Step S3) In this step, the processing unit 25 uses the measured power of the emitted light to determine the magnitude of crosstalk between the core 11 and the core 12, in the same manner as in the first embodiment. Furthermore, in this step of the present embodiment, the processing unit 25 determines the magnitude of crosstalk between the core 12 and the core 13. The method for determining the crosstalk between the core 12 and the core 13 is the same as the method for determining the crosstalk between the core 11 and the core 13 in the third embodiment.

[0124] The processing unit 25 converts the power of the crosstalk light CL1 determined in the same manner as in the first embodiment into the magnitude of crosstalk and outputs the converted value, and also converts the power of the crosstalk light CL2 determined into the magnitude of crosstalk and outputs the converted value. At this time, the processing unit 25 may convert the magnitude of crosstalk into decibels indicating the ratio to the power of the incident light L emitted from the other end 18 of the core 13 and output the converted value. The processing unit 25 may also convert the magnitude of crosstalk into decibels indicating the ratio to a predetermined power determined in the OTDR 20 and output the converted value. In this way, the magnitude of crosstalk between the core 11 and the core 12 and the magnitude of crosstalk between the core 11 and the core 13 are determined.

[0125] In the crosstalk measurement method of this embodiment, in addition to the crosstalk measurement method of the first embodiment, in the connection step S1, one end 17 of the core 12 and one end 17 of the core 13 are further optically connected via the core of the second optical fiber 52, and in the first measurement step S2, the power of the output light that includes pulsed light generated by combining light generated when the incident light L crosstalks from the core 12 to the core 13 and light generated when the incident light L that enters the core 12 from the core 13 via the core of the second optical fiber 52 crosstalks from the core 13 to the core 12 is further measured by the OTDR 20, and that exits from the one end 17 of the core 11 via the first optical fiber 51 and the core 11, and in the processing step S3, the magnitude of the crosstalk between the core 12 and the core 13 is further determined using the power of the output light that includes pulsed crosstalk light CL2 generated by the crosstalk between the core 12 and the core 13.

[0126] In addition to the components of the crosstalk measurement device 1 of the first embodiment, the crosstalk measurement device 1 of this embodiment further includes a core of a second optical fiber 52 that optically connects one end 17 of the core 12 and one end 17 of the core 13, and the OTDR 20 includes pulsed light that is a combination of light generated by crosstalk of the incident light L from the core 12 to the core 13 and light generated by crosstalk from the core 13 to the core 12 of the incident light L that enters the core 12 from the core 13 via the core of the second optical fiber 52, and further measures the power of the output light that is output from the one end 17 of the core 11 via the first optical fiber 51 and the core 11, and the processing unit 25 further determines the magnitude of the crosstalk between the core 12 and the core 13 using the power of the output light that includes pulsed crosstalk light CL2 generated by the crosstalk between the core 12 and the core 13.

[0127] According to the crosstalk measurement method and crosstalk measurement device 1 of this embodiment, the output light including crosstalk light between core 11 and core 12 and the output light including crosstalk light between core 12 and core 13 are each received by OTDR 20, the power of each output light can be measured, and the magnitude of each crosstalk can be determined. Therefore, compared to the case in which the magnitude of crosstalk between core 11 and core 12 is measured as in the first embodiment, and then core 12 and core 13 are optically connected by a connecting optical waveguide and incident light is again made incident from one end 17 of core 11 to measure the magnitude of crosstalk between core 12 and core 13, the magnitude of crosstalk between core 11 and core 12 and the magnitude of crosstalk between core 12 and core 13 can each be easily measured.

[0128] 9 , a second measurement step S22 may be provided after the first measurement step S2. In this case, in the second measurement step S22, pulsed incident light L output from the OTDR 20 is input from the other end 18 of the core 13. The OTDR 20 measures the power of the output light output from the other end 18 of the core 13, which includes pulsed light obtained by combining light generated by crosstalk of the incident light L from the core 13 to the core 12 and light generated by crosstalk of the incident light L entering the core 12 from the core 13 via the second optical fiber 52. Furthermore, the OTDR 20 measures the power of output light that includes pulsed light generated by crosstalk from core 12 to core 11 while the incident light L is propagating through the core 12 from one end 17 to the other end 18, and light generated by crosstalk from core 11 to core 12 of the incident light L that enters the core 11 via the first optical fiber 51. The output light travels from one end 17 of the core 12 through the second optical fiber 52 and the core 13 and is output from the other end 18 of the core 13. In this case, in processing step S3, the magnitude of crosstalk between the core 12 and the core 13 is determined using the power of the output light measured in the first measurement step S2 and the power of the output light measured in the second measurement step S22, as in the second embodiment.

[0129] Fifth Embodiment Next, a fourth embodiment of the present invention will be described in detail with reference to Fig. 14. Note that components that are the same as or equivalent to those in the above-described embodiments will be assigned the same reference numerals and redundant description will be omitted unless otherwise specified.

[0130] 14 is a diagram illustrating the crosstalk measurement device of this embodiment, following the example of FIG. 4. The crosstalk measurement device 1 of this embodiment differs from the crosstalk measurement device 1 of the first embodiment in that it includes a second optical fiber 52 as a second connection waveguide, and one end 17 of the core 12, which is the second optical waveguide, and the other end of the core 13, which is the third optical waveguide, are optically connected via the second optical fiber 52. In this embodiment, the lengths of the first optical fiber 51 and the second optical fiber 52 may be different from each other or may be the same.

[0131] The procedure of the crosstalk measurement method of this embodiment using such a crosstalk measurement device 1 is the same as that shown in the flowchart of Fig. 3. However, each step differs as follows. The differences will be mainly explained below.

[0132] (Connection Step S1) In this step of the present embodiment, in addition to the connection step S1 of the first embodiment, one end 17 of the core 12 and the other end 18 of the core 13 are optically connected via the core of the second optical fiber 52. Specifically, one end of the second optical fiber 52 is connected to the optical fiber 32 of the fan-in-fan-out device 30, and the other end of the second optical fiber 52 is connected to the optical fiber 43 of the fan-in-fan-out device 40. In this way, the core 12 and the core 13 are optically connected.

[0133] (First measurement step S2) In this step of the present embodiment, as in the first embodiment, incident light L is incident on the core 11 from the OTDR 20. In this embodiment, in addition to the crosstalk between the core 11 and the core 12 described in the first embodiment, crosstalk occurs as follows, and this crosstalk is measured. This will be described below.

[0134] The incident light L entering the core 11 from the OTDR 20 propagates through the core 11 from one end 17 to the other end 18, crosstalking from the core 11 to the core 12 and also propagating from the core 11 to the core 13. The light crosstalking from the core 11 to the core 13 also takes the form of pulses, and propagates from the one end 17 to the other end 18 of the core 13 while traveling generally parallel to the incident light L. The power of this crosstalk light CL2 increases according to the distance it propagates through the core 13. The incident light L and the crosstalk light CL2 reach the other end 18 at roughly the same time. The incident light L enters the core 13 from the other end 18 of the core 11 via the first optical fiber 51, the core 12, and the second optical fiber 52. Furthermore, crosstalk light CL2 enters the core 11 from the other end 18 of the core 13 via the second optical fiber 52, the core 12, and the first optical fiber 51. The incident light L and the crosstalk light CL2 intersect at approximately the midpoint of the waveguide formed by the core of the first optical fiber 51, the core 12, and the core of the second optical fiber 52. Therefore, the timing at which the incident light L enters the core 13 and the timing at which the crosstalk light CL2 enters the core 11 are approximately the same. The incident light L that entered the core 13 and the crosstalk light CL2 that entered the core 11 travel approximately parallel to each other and propagate through the respective cores 13 and 11 from the other end 18 to the one end 17. During this time, the incident light L propagating through the core 13 propagates while causing crosstalk to the core 11. Therefore, light that crosstalks from core 13 to core 11 is multiplexed with crosstalk light CL2 propagating through core 11. The multiplexed light is pulsed and propagates while gradually increasing in power. Outgoing light, in which this pulsed crosstalk light CL2 is multiplexed with light such as backscattered light, is emitted from one end 17 of core 11. Therefore, the outgoing light includes pulsed crosstalk light CL2. The outgoing light from core 11 enters OTDR 20, is received by OTDR 20, and its power is measured by OTDR 20.

[0135] The timing at which the output light including the crosstalk light CL2 enters the OTDR 20 is delayed relative to the timing at which the output light including the crosstalk light CL1 enters the OTDR 20 by the time it takes for the light to propagate through the second optical fiber 52 and the core 13. Therefore, the OTDR 20 can measure each of these output lights. Therefore, the OTDR 20 measures the power of the pulsed light twice.

[0136] (Processing Step S3) In this step, the processing unit 25 uses the measured power of the emitted light to determine the magnitude of crosstalk between the core 11 and the core 12 in the same manner as in the first embodiment. Furthermore, in this step of the present embodiment, the processing unit 25 determines the magnitude of crosstalk between the core 11 and the core 13. The method for determining the crosstalk between the core 11 and the core 13 is the same as the method for determining the crosstalk between the core 11 and the core 13 in the third embodiment.

[0137] The processing unit 25 converts the power of the crosstalk light CL1 determined in the same manner as in the first embodiment into the magnitude of crosstalk and outputs the converted value, and also converts the power of the crosstalk light CL2 determined into the magnitude of crosstalk and outputs the converted value. At this time, the processing unit 25 may convert the magnitude of crosstalk into decibels indicating the ratio to the power of the incident light L emitted from one end 17 of the core 13 and output the converted value. The processing unit 25 may also convert the magnitude of crosstalk into decibels indicating the ratio to a predetermined power determined in the OTDR 20 and output the converted value. In this way, the magnitude of crosstalk between the core 11 and the core 12 and the magnitude of crosstalk between the core 11 and the core 13 are determined.

[0138] In the crosstalk measurement method of this embodiment, in addition to the crosstalk measurement method of the first embodiment, in the connection step S1, one end 17 of the core 12 and the other end 18 of the core 13 are further optically connected via the core of the second optical fiber 52, and in the first measurement step S2, the power of the output light output from one end 17 of the core 11 is further measured by the OTDR 20, which includes pulsed light that is a combination of light generated by crosstalk of the incident light L from the core 11 to the core 13 and light generated by crosstalk from the core 13 to the core 11 of the incident light L that enters the core 11 from the core 13 via the core 12 and the core of the second optical fiber 52, and in the processing step S3, the magnitude of the crosstalk between the core 11 and the core 13 is further determined using the power of the output light including the pulsed crosstalk light CL2 generated by the crosstalk between the core 11 and the core 13.

[0139] In addition to the components of the crosstalk measuring device 1 of the first embodiment, the crosstalk measuring device 1 of this embodiment further includes a core of a second optical fiber 52 that optically connects one end 17 of the core 12 and the other end 18 of the core 13, and the OTDR 20 includes pulsed light that is a combination of light generated by crosstalk of the incident light L from the core 11 to the core 13 and light generated by crosstalk from the core 13 to the core 11 of the incident light L that enters the core 11 from the core 13 via the core 12 and the core of the second optical fiber 52, and further measures the power of the output light that is output from the one end 17 of the core 11, and the processing unit 25 further determines the magnitude of the crosstalk between the core 11 and the core 13 using the power of the output light that includes pulsed crosstalk light CL2 generated by the crosstalk between the core 11 and the core 13.

[0140] According to the crosstalk measurement method and crosstalk measurement device 1 of this embodiment, the output light including crosstalk light between core 11 and core 12 and the output light including crosstalk light between core 11 and core 13 are each received by OTDR 20, the power of each output light can be measured, and the magnitude of each crosstalk can be determined. Therefore, compared to the case in which the magnitude of crosstalk between core 11 and core 12 is measured as in the first embodiment, and then core 11 and core 13 are optically connected by a connecting optical waveguide and incident light is again made incident from one end 17 of core 11 to measure the magnitude of crosstalk between core 11 and core 13, the magnitude of crosstalk between core 11 and core 12 and the magnitude of crosstalk between core 11 and core 13 can each be easily measured.

[0141] 9 , a second measurement step S22 may be provided after the first measurement step S2. In this case, in the second measurement step S22, pulsed incident light L output from the OTDR 20 is input from one end 17 of the core 13. The OTDR 20 measures the power of the output light output from the one end 17 of the core 13, which includes pulsed light obtained by combining light generated by crosstalk of the incident light L from the core 13 to the core 11 and light generated by crosstalk of the incident light L entering the core 11 from the core 13 via the second optical fiber 52, the core 12, and the first optical fiber 51. Furthermore, the OTDR 20 measures the power of output light that includes pulsed light generated by crosstalk from core 12 to core 11 while the incident light L is propagating through the core 12 from one end 17 to the other end 18, and light generated by crosstalk from core 11 to core 12 of the incident light L that enters the core 11 via the first optical fiber 51. The output light travels from one end 17 of the core 12 through the second optical fiber 52 and the core 13 and is output from one end 17 of the core 13. In this case, in processing step S3, the magnitude of crosstalk between the core 11 and the core 13 is determined using the power of the output light measured in the first measurement step S2 and the power of the output light measured in the second measurement step S22, as in the second embodiment.

[0142] Although the present invention has been described above using the above-mentioned embodiments as examples, the present invention is not limited to these.

[0143] For example, the arrangement and number of cores in the multicore fiber 10 may be different from those in the above embodiment.

[0144] Although the above embodiment has been described using a multicore fiber as an example of an optical device in which waveguides are arranged in parallel, the optical device of the present invention is not limited to a multicore 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.

[0145] Furthermore, in at least one of the first measurement step S2 and the second measurement step S22 of the above embodiment, the OTDR 20 may further measure at least one of the optical loss, reflection intensity, bending loss, and breakage in an optical device such as the multi-core fiber 10.

[0146] Furthermore, there are no particular limitations on the form of the fan-in-fan-out devices 30, 40. Furthermore, the crosstalk measurement device 1 does not need to include at least one of the fan-in-fan-out devices 30, 40. In this case, for example, the core of the multicore fiber 10 is directly connected to the core of the first optical fiber 51 or the core of the second optical fiber 52. Furthermore, at least one of the first optical fiber 51 and the second optical fiber 52 may be formed from a connection body of a plurality of optical fibers.

[0147] In the above embodiment, for example, as shown in Fig. 5 , the gradient of the power of the backscattered light measured by the OTDR 20 is approximately the same in sections such as the core 11, the core 12, and the first optical fiber 51. This indicates that the loss of incident light L per unit length due to backscattering is approximately the same in sections such as the core 11, the core 12, and the first optical fiber 51. Therefore, in the above embodiment, when light of the same power is propagated through the core 11, the core 12, and the first optical fiber 51, 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, the core 12, and the first optical fiber 51, it is preferable that the power of the backscattered light per unit length generated in the first optical fiber 51 is smaller than the power of the backscattered light per unit length generated in each of the cores 11 and 12. An example of such a first optical fiber 51 is a hollow-core optical fiber having a hollow core. Alternatively, the first optical fiber 51 may be an optical fiber whose core has a smaller relative refractive index difference than the light propagating through the core of the multicore fiber 10 and whose effective cross-sectional area for 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. FIG. 15 is a schematic diagram showing measurement results with the OTDR 20 when a hollow-core optical fiber is used as the first optical fiber 51 in FIG. 4 . However, FIG. 15 is a schematic diagram showing measurement results when a two-core multicore fiber is used. As shown in FIG. 15 , it can be seen that almost no backscattered light is generated in the first optical fiber 51. Therefore, the ratio of the power of crosstalk light to the power of backscattered light is increased, making it easier to detect crosstalk light. Note that, for the same reasons as above, it is preferable that the power of the backscattered light per unit length generated in the second optical fiber 52 of the third to fifth embodiments is smaller than the power of the backscattered light per unit length generated in each of the cores 11 to 13.

[0148] In the first embodiment, the cores 13 and 14 are not connected to each other by optical fibers, as shown in FIGS. 2 and 4 . However, the present invention is not limited to this. FIG. 16 is a diagram showing a modification of the crosstalk measurement device of the first embodiment. As shown in FIG. 16 , this modification differs from the first embodiment in that the optical fibers 43 and 44 of the fan-in-fan-out device 40 are connected to a second optical fiber 52, and the other end 18 of the core 13 and the other end 18 of the core 14 are optically connected via the core of the second optical fiber 52. The length of the second optical fiber 52 is the same as that of the first optical fiber 51. Therefore, the distance light propagates from the other end 18 of the core 13 to the other end 18 of the core 14 is the same as the distance light propagates from the other end 18 of the core 11 to the other end 18 of the core 12. In the first embodiment, pulsed light resulting from crosstalk light CL1 of incident light crosstalking from core 11 to core 12 and crosstalk light CL1 of incident light crosstalking from core 12 to core 11 was measured. However, the crosstalk light CL1 of crosstalking from core 11 to core 12 also includes light that crosstalks from core 11 to cores 13 and 14 and then crosstalks to core 12. Similarly, the light that crosstalks from core 12 to core 11 also includes light that crosstalks from core 12 to cores 13 and 14 and then crosstalks to core 11. In the first embodiment, because there is no optical connection between core 13 and core 14, the light that crosstalks from core 11 to cores 13 and 14 and does not further crosstalk to core 12 is emitted from the other end 18. However, according to this modification, of the light that crosstalks from core 11 to core 13, the light that does not further crosstalk to core 12 enters core 14 via the second optical fiber 52, and of the light that crosstalks from core 11 to core 14, the light that does not further crosstalk to core 12 enters core 13 via the second optical fiber 52. The light that entered cores 13, 14 via the second optical fiber 52 further crosstalks to core 12 when propagating through cores 13, 14 from the other end 18 side to the one end 17 side.Furthermore, as described above, the distance that light propagates from the other end 18 of core 13 to the other end 18 of core 14 is the same as the distance that light propagates from the other end 18 of core 11 to the other end 18 of core 12, and therefore the timing at which crosstalk light CL1 emitted from the other end of core 12 enters the other end of core 11 is approximately the same as the timing at which light that crosstalks from core 11 to cores 13 and 14 but does not further crosstalk to core 12 enters cores 14 and 13 via the second optical fiber 52. With this configuration, light that crosstalks to core 12 via cores 13 and 14 is reflected as crosstalk light CL1 on both the outbound and inbound paths. Therefore, in this modified example, the other ends 18 of core 13, which is the third waveguide, and core 14, which is the fourth waveguide, which crosstalk with core 11, which is the first optical waveguide, and core 12, which is the second optical waveguide, respectively, are optically connected via the core of second optical fiber 52, which is the second connecting optical waveguide, so that the magnitude of crosstalk can be measured more accurately than in the first embodiment.

[0149] As described above, according to the present invention, a crosstalk measurement method and a crosstalk measurement device that can easily measure crosstalk using the OTDR method are provided, and it is expected that these will be used in fields such as optical fiber communications.

Claims

1. A method for measuring crosstalk in an optical device having a first optical waveguide and a second optical waveguide arranged in parallel with each other and including one end and the other end, comprising: a connecting step of optically connecting the other end of the first optical waveguide and the other end of the second optical waveguide via a first connecting optical waveguide; a first measuring step of making a pulsed incident light output from an OTDR (Optical Time Domain Reflectometer) enter the first optical waveguide from the one end, and measuring the power of an output light output from the one end of the first optical waveguide by the OTDR, the output light including a pulsed light obtained by combining a light generated by crosstalk of the incident light from the first optical waveguide to the second optical waveguide and a light generated by crosstalk of the incident light input from the first optical waveguide to the second optical waveguide via the first connection optical waveguide from the first optical waveguide to the second optical waveguide; a processing step of determining a magnitude of crosstalk between the first optical waveguide and the second optical waveguide using the measured power of the emitted light; Equipped 13. A crosstalk measuring method comprising:

2. The length of the first connection optical waveguide is longer than the half-width of the incident light.

2. The crosstalk measuring method according to claim 1 .

3. a second measuring step of making a pulsed incident light output from the OTDR incident from one end of the second optical waveguide, the second optical waveguide including a pulsed light generated by crosstalk of the incident light from the second optical waveguide to the first optical waveguide, and a pulsed light generated by crosstalk of the incident light input from the second optical waveguide to the first optical waveguide via the first connection optical waveguide from the second optical waveguide to the first optical waveguide, the second optical waveguide including a pulsed light combined, the first optical waveguide including a pulsed light generated by crosstalk of the incident light input from the second optical waveguide to the first optical waveguide via the first connection optical waveguide, the first optical waveguide including a pulsed light, the second optical waveguide including a pulsed light In the processing step, the magnitude of the crosstalk between the first optical waveguide and the second optical waveguide is obtained using the power of the emitted light measured in the first measurement step and the power of the emitted light measured in the second measurement step.

2. The crosstalk measuring method according to claim 1 .

4. In the processing step, the magnitude of the crosstalk between the first optical waveguide and the second optical waveguide is obtained using an average result of the power of the emitted light measured in the first measuring step and the power of the emitted light measured in the second measuring step.

4. The crosstalk measuring method according to claim 3.

5. The wavelength width of the incident light is 1 nm or more.

2. The crosstalk measuring method according to claim 1 .

6. the OTDR and the first optical waveguide, the first optical waveguide and the first connecting optical waveguide, and the first connecting optical waveguide and the second optical waveguide are optically connected by a fan-in-fan-out device; In the processing step, a magnitude of crosstalk in the fan-in-fan-out device is removed, and a magnitude of the crosstalk between the first optical waveguide and the second optical waveguide is obtained.

6. The crosstalk measuring method according to claim 1, wherein the crosstalk measuring method is a method for measuring a crosstalk frequency.

7. the optical device further includes a third optical waveguide arranged in parallel with the first optical waveguide; In the processing step, a magnitude of crosstalk between the first optical waveguide and the third optical waveguide is further obtained based on the obtained magnitude of crosstalk between the first optical waveguide and the second optical waveguide.

6. The crosstalk measuring method according to claim 1, wherein the crosstalk measuring method is a method for measuring a crosstalk frequency.

8. the optical device further includes a third optical waveguide arranged in parallel with the first optical waveguide; In the connecting step, the other end of the first optical waveguide and the other end of the third optical waveguide are optically connected via a second connecting optical waveguide having a length different from that of the first connecting optical waveguide, the first measuring step further measures a power of an output light output from the one end of the first optical waveguide by the OTDR, the output light including a pulsed light generated by combining light generated by crosstalk of the incident light from the first optical waveguide to the third optical waveguide and light generated by crosstalk of the incident light input from the first optical waveguide to the third optical waveguide via the second connection optical waveguide to the first optical waveguide; In the processing step, a magnitude of crosstalk between the first optical waveguide and the third optical waveguide is further obtained using the power of the emitted light including pulsed light caused by crosstalk between the first optical waveguide and the third optical waveguide.

6. The crosstalk measuring method according to claim 1, 2 or 5.

9. the optical device further includes a third optical waveguide arranged in parallel with the second optical waveguide; The connecting step further comprises optically connecting one end of the second optical waveguide and one end of the third optical waveguide via a second connecting optical waveguide; the first measuring step further measures, by the OTDR, a power of output light output from the one end of the first optical waveguide via the first connection optical waveguide and the first optical waveguide, the power of output light including a pulsed light generated by combining light generated by crosstalk from the second optical waveguide to the third optical waveguide, of the incident light input from the first optical waveguide to the second optical waveguide via the first connection optical waveguide, and light generated by crosstalk from the third optical waveguide to the second optical waveguide, of the incident light input from the second optical waveguide to the third optical waveguide via the second connection optical waveguide; In the processing step, a magnitude of crosstalk between the second optical waveguide and the third optical waveguide is further obtained using the power of the emitted light including pulsed light caused by crosstalk between the second optical waveguide and the third optical waveguide.

6. The crosstalk measuring method according to claim 1, 2 or 5.

10. the optical device further includes a third optical waveguide arranged in parallel with the first optical waveguide; The connecting step further comprises optically connecting one end of the second optical waveguide and the other end of the third optical waveguide via a second connecting optical waveguide; the first measuring step further measures a power of an output light output from the one end of the first optical waveguide by the OTDR, the power of the output light including a pulsed light generated by combining light generated by crosstalk from the first optical waveguide to the third optical waveguide, and light generated by crosstalk from the third optical waveguide to the first optical waveguide, the input light input from the first optical waveguide to the third optical waveguide via the first connection optical waveguide, the second optical waveguide, and the second connection optical waveguide; In the processing step, a magnitude of crosstalk between the first optical waveguide and the third optical waveguide is further obtained using the power of the emitted light including pulsed light caused by crosstalk between the first optical waveguide and the third optical waveguide.

6. The crosstalk measuring method according to claim 1, 2 or 5.

11. In the first measuring step, at least one of an optical loss, a reflection intensity, a bending loss, and a break in the optical device is further measured by the OTDR.

6. The crosstalk measuring method according to claim 1, 2 or 5.

12. When light having the same power is propagated through the first optical waveguide, the second optical waveguide, and the first connecting optical waveguide, the power of backscattered light per unit length generated in the first connecting optical waveguide is smaller than the power of backscattered light per unit length generated in each of the first optical waveguide and the second optical waveguide.

6. The crosstalk measuring method according to claim 1, 2 or 5.

13. An apparatus for measuring crosstalk of an optical device having a first optical waveguide and a second optical waveguide arranged in parallel with each other and including one end and the other end, a first connecting optical waveguide that optically connects the other end of the first optical waveguide and the other end of the second optical waveguide; an OTDR that makes a pulsed incident light incident on the one end of the first optical waveguide, and measures the power of an output light output from the one end of the first optical waveguide, the output light including a pulsed light obtained by combining a light generated by crosstalk of the incident light from the first optical waveguide to the second optical waveguide and a light generated by crosstalk of the incident light, which is input from the first optical waveguide to the second optical waveguide via the first connection optical waveguide, to the first optical waveguide; a processing unit that calculates a magnitude of crosstalk between the first optical waveguide and the second optical waveguide using the measured power of the emitted light; Equipped A crosstalk measuring device comprising: