Crosstalk measurement method and crosstalk measurement apparatus

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

[Technical Field] 【0001】 This invention relates to a crosstalk measurement method and a crosstalk measurement apparatus. [Background technology] 【0002】 In recent years, the increasing volume of information and communication has necessitated an expansion of optical fiber transmission capacity. Multicore fibers are attracting attention because they can improve space utilization efficiency and enable high-capacity information transmission in limited spaces. However, because multiple cores are arranged in a single optical fiber, evaluating their characteristics is more difficult than with single-core fibers. Therefore, there is a need for technology to efficiently evaluate multicore fibers. In particular, crosstalk measurement is an important measurement item for multicore fibers, and since it is not a measurement item for single-core fibers, it is necessary to prepare new measurement equipment. 【0003】 The following methods described in the non-patent documents are known as crosstalk measurement methods. Non-patent document 1 describes the PM (Power Meter) method. The PM method involves injecting light into a predetermined core of a multicore fiber from one end and measuring the power of the light emitted from the other end of the core that crosstalks with this core. Non-patent documents 2 and 3 describe the OTDR (Optical Time Domain Reflectometer) method. In the OTDR method, a multi-channel OTDR is used to inject light into a predetermined core, and the backscattered light that crosstalks with other cores is detected to measure the crosstalk. 【0004】 [Non-Patent Document 1] [1] K. Takenaga, Y. Arakawa, S. Tanigawa, N. Guan, S. Matsuo, K. Saitoh and M. Koshiba, “An Investigation on Crosstalk in Multi-Core Fibers by Introducing Random Fluctuation along Longitudinal Direction,” IEICE TRAN. COMMUN., Vol.E94-B, No.2, 2011. [Non-Patent Document 2] [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 [Non-Patent Document 3] [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 [Summary of the Invention] 【0005】 In the PM method, it is necessary to inject light from one end of a multicore fiber and receive the light that exits from the other end. In contrast, in the OTDR method, light is injected from one end of a multicore fiber and received the light that exits from the same end. Therefore, 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 the backscattered light after crosstalk, so there is a concern that the power of the light being measured is small and it is difficult to measure crosstalk. For multicore fibers of a type with small crosstalk, measuring crosstalk is even more difficult. However, as mentioned above, there is a need to measure crosstalk using the OTDR method. Such a need can arise not only for multicore fibers but also for optical devices having multiple optical waveguides where crosstalk can occur. 【0006】 Therefore, the present invention aims to provide a crosstalk measurement method and a crosstalk measurement apparatus that can easily measure crosstalk using the OTDR method. 【0007】 To solve the above problems, aspect 1 of the present invention is a method for measuring crosstalk in an optical device having a first optical waveguide and a second optical waveguide that are parallel to each other and include one end and the other end, comprising a connection 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 a pulsed incident light emitted from an OTDR is incident from the one end of the first optical waveguide, and the light generated by the crosstalk of the incident light from the first optical waveguide to the second optical waveguide and the first connecting The crosstalk measurement method is characterized by comprising: a first measurement step of measuring the power of emitted light emitted from one end of the first optical waveguide using the OTDR, which includes pulsed light resulting from the crosstalk between the incident light incident light incident from the first optical waveguide to the second optical waveguide via the optical waveguide and the light generated by the crosstalk from the second optical waveguide to the first optical waveguide; and a processing step of determining the magnitude of the crosstalk between the first optical waveguide and the second optical waveguide using the measured power of the emitted light. 【0008】 A pulsed incident light propagating from one end of the first optical waveguide to the other propagates through the second optical waveguide while crosstalking. Consequently, the crosstalk light crosstalking from the first optical waveguide to the second optical waveguide is also pulsed and propagates from one end of the second optical waveguide to the other, generally parallel to the incident light. The incident light reaching the other end of the first optical waveguide is incident on the first connecting optical waveguide. Similarly, pulsed crosstalk light propagating from one end of the second optical waveguide and reaching the other end of the second optical waveguide is incident on the first connecting optical waveguide from the opposite side of the incident light. Since 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 arrive at the other ends of the first and second optical waveguides approximately simultaneously, and the incident light and the crosstalk light pass each other approximately at the midpoint of the first connecting optical waveguide. 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 of the incident light entering the second optical waveguide and the timing of the crosstalk light entering the first optical waveguide are approximately the same. For this reason, the crosstalk light propagates through the first optical waveguide from one end to the other, while generally running parallel to the incident light propagating through the second optical waveguide from one end to the other. During this time, the incident light propagating through the second optical waveguide also propagates through the first optical waveguide while crosstalking with it. Therefore, light crosstalking from the second optical waveguide to the first optical waveguide combines with the crosstalk light propagating through the first waveguide. The combined light is pulsed, and the emitted light from one end of the first optical waveguide includes pulsed light generated by the crosstalk. The light emitted from the first optical waveguide is received by an OTDR, and the power of the emitted light is measured. This measured power of the emitted light is used to determine the magnitude of the crosstalk between the first and second optical waveguides. 【0009】 Thus, according to the crosstalk measurement method of this embodiment, since the light incident on an optical waveguide using an OTDR is used as the crosstalk light to another optical waveguide, the power of the crosstalk light is greater compared to the case where backscattered light of crosstalk is detected as in Patent Documents 2 and 3. Furthermore, in the crosstalk measurement method of this embodiment, the crosstalk light when the incident light propagates from one end to the other of the first optical waveguide and the crosstalk light when the incident light propagates from the other end to the one end of the second optical waveguide are combined, so the power of the pulsed light generated by crosstalk tends to be large. Therefore, according to the crosstalk measurement method of this embodiment, crosstalk can be easily measured. 【0010】 Aspect 2 of the present invention is a crosstalk measurement method according to aspect 1, characterized in that the length of the first connecting optical waveguide is longer than the half-width of the incident light. 【0011】 As described above, the incident light and the crosstalk light pass each other approximately at the midpoint of the first connecting optical waveguide. Therefore, in an OTDR, the pulsed light generated by crosstalk appears to originate approximately at the midpoint of the first connecting optical waveguide. Furthermore, the pulse width of the incident light and the pulse width of the crosstalk light are approximately the same. Accordingly, the crosstalk measurement method of this embodiment can suppress the influence of noise such as reflections at the ends of the first connecting optical waveguide on the emitted light including pulsed crosstalk light, and crosstalk can be measured more accurately. 【0012】 A third aspect of the present invention is a crosstalk measurement method according to aspect 1 or 2, characterized in that pulsed incident light emitted from the OTDR is incident on the second optical waveguide from one end, and the pulsed light is obtained by combining the light generated when the incident light crosstalks from the second optical waveguide to the first optical waveguide and the incident light incident on the first optical waveguide from the second optical waveguide to the first optical waveguide via the first connecting optical waveguide, and the power of the emitted light emitted from the one end of the second optical waveguide is measured with the OTDR, and in the processing step, the magnitude of the crosstalk between the first optical waveguide and the second optical waveguide is determined 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. 【0013】 In this case, since we use 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, we can suppress errors and determine the crosstalk more accurately compared to the case where we only use the crosstalk light generated by propagating incident light from the first optical waveguide to the second optical waveguide. 【0014】 Aspect 4 of the present invention is a crosstalk measurement method of aspect 3, 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 emitted light measured in the first measurement step and the power of the emitted light measured in the second measurement step. 【0015】 By using this averaging process, the magnitude of crosstalk can be easily and accurately determined. 【0016】 Aspect 5 of the present invention is a crosstalk measurement method according to any one of aspects 1 to 4, characterized in that 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】 Aspect 6 of the present invention is a crosstalk measurement method according to any one of aspects 1 to 5, 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 in the processing step, the magnitude of the crosstalk in the fan-in-fan-out device is removed and the magnitude of the crosstalk between the first optical waveguide and the second optical waveguide is determined. 【0019】 In this case, the effects of crosstalk in a fan-in / fan-out device can be suppressed, and the crosstalk can be determined more accurately. 【0020】 Aspect 7 of the present invention is a crosstalk measurement method according to any one of aspects 1 to 6, 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 and third optical waveguides can be easily determined without measuring the optical power due to the crosstalk between the first and third optical waveguides. Specifically, in this case, the magnitude of the crosstalk between the first and third optical waveguides can be determined using a relational expression that shows the relationship between the magnitude of the crosstalk between the first and second optical waveguides and the magnitude of the crosstalk between the first and third optical waveguides. 【0022】 Aspect 8 of the present invention further comprises a third optical waveguide parallel to the first optical waveguide, wherein in the connection 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 of a different length from the first connecting optical waveguide, and in the first measurement step, the light generated by the crosstalk of the incident light from the first optical waveguide to the third optical waveguide and the incident light entering the third optical waveguide from the first optical waveguide via the second connecting optical waveguide are The crosstalk measurement method is one of embodiments 1 to 6, characterized in that the power of the emitted light, which includes light generated by crosstalk from the third optical waveguide to the first optical waveguide and pulsed light formed by the combination of these, 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 emitted light, which includes pulsed light generated by crosstalk between the first optical waveguide and the third optical waveguide. 【0023】 In this case, as described in Embodiment 1, crosstalk occurs between the first optical waveguide and the second optical waveguide, and emitted light including pulsed light due to this crosstalk is emitted from one end of the first optical waveguide. Furthermore, in this embodiment, crosstalk occurs between the first optical waveguide and the third optical waveguide, and emitted light including pulsed light due to this crosstalk is emitted from one end of the first optical waveguide. At this time, since the first connecting optical waveguide and the second connecting optical waveguide are of 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 emitted from one end of the first optical waveguide at different timings. Therefore, by receiving the emitted light containing pulsed light due to crosstalk between the first and second optical waveguides, and the emitted light containing pulsed light due to crosstalk between the first and third optical waveguides, with an OTDR, the power of each emitted light can be measured, and the magnitude of each crosstalk can be determined. Thus, compared to the case in Embodiment 1, where the crosstalk between the first and second optical waveguides is measured, and then the first and third optical waveguides are optically connected with a connecting optical waveguide, and incident light is again incident from one end of the first optical waveguide to measure the crosstalk between the first and third optical waveguides, the crosstalk between the first and second optical waveguides, and the crosstalk between the first and third optical waveguides can be easily measured. 【0024】 In embodiment 8, it is preferable that the difference between the length of the first connecting optical waveguide and the length of the second connecting optical waveguide is greater than the full width at half maximum of the incident light. 【0025】 In this case, interference between pulsed light resulting from crosstalk between the first and second optical waveguides and pulsed light resulting from crosstalk between the first and third optical waveguides can be suppressed, allowing for more accurate measurement of the magnitude of the crosstalk. 【0026】 Aspect 9 of the present invention further comprises a third optical waveguide parallel to the second optical waveguide, wherein in the connection step, one end of the second optical waveguide and one end of the third optical waveguide are optically connected via a second connecting optical waveguide, and in the first measurement step, the light generated by the crosstalk of the incident light entering the second optical waveguide from the first optical waveguide through the first connecting optical waveguide to the third optical waveguide, and the incident light entering the third optical waveguide from the second optical waveguide through the second connecting optical waveguide, are transmitted to the third optical waveguide. The crosstalk measurement method according to any of embodiments 1, 2, 5, or 6 is characterized in that the power of the emitted light, which includes light generated by crosstalk from the waveguide to the second optical waveguide and pulsed light resulting from the combination of these, 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 emitted light, which includes pulsed light generated by crosstalk between the second optical waveguide and the third optical waveguide. 【0027】 In this case, as described in Embodiment 1, crosstalk occurs between the first optical waveguide and the second optical waveguide, and the emitted light, including pulsed light due to this crosstalk, is emitted from one end of the first optical waveguide. Furthermore, in this embodiment, pulsed incident light that enters 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, the crosstalk light that crosstalks from the second optical waveguide to the third optical waveguide is also pulsed and propagates from the other end to one end of the third optical waveguide, generally running parallel to the incident light. The incident light that reaches one end of the second optical waveguide enters the second connecting optical waveguide. Also, the crosstalk light that reaches one end of the third optical waveguide enters the second connecting optical waveguide from the opposite side of the incident light. As described above, the propagation speed of incident light and the propagation speed of crosstalk light are equal to each other. Therefore, the incident light and crosstalk light, which arrive at one end approximately simultaneously, pass each other 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 of the incident light entering the third optical waveguide and the timing of the crosstalk light entering the second optical waveguide are approximately the same. For this reason, the crosstalk light propagates through the second optical waveguide from one end to the other, roughly parallel to the incident light propagating through the third optical waveguide from one end to the other. During this time, the incident light propagating through the third optical waveguide also propagates through the second optical waveguide while crosstalking. Consequently, light crosstalking from the third optical waveguide to the second optical waveguide combines with the crosstalk light propagating through the second waveguide. The combined light is pulsed, and the emitted light from one end of the first optical waveguide via the first connecting optical waveguide and the first optical waveguide includes pulsed light generated by the crosstalk between the second and third optical waveguides. The emitted light from the first optical waveguide is received by an OTDR, and the power of this emitted light is measured. 【0028】 At this time, pulsed light resulting from crosstalk between the first and second optical waveguides, and pulsed light resulting from crosstalk between the second and third optical waveguides, are emitted from one end of the first optical waveguide at different timings. Therefore, by receiving the emitted light containing the light from the crosstalk between the first and second optical waveguides, and the emitted light containing the light from the crosstalk between the second and third optical waveguides, respectively, with an OTDR, the power of each emitted light can be measured, and the magnitude of each crosstalk can be determined. Therefore, compared to the case in Embodiment 1, where the crosstalk between the first optical waveguide and the second optical waveguide is measured, and then the other end of the second optical waveguide and the other end of the third optical waveguide are optically connected with a connecting optical waveguide, and incident light is again 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】 Aspect 10 of the present invention further comprises a third optical waveguide parallel to the first optical waveguide, wherein in the connection step, one end of the second optical waveguide and the other end of the third optical waveguide are optically connected via a second connecting optical waveguide, and in the first measurement step, the light generated by the crosstalk of the incident light entering the first optical waveguide from the OTDR into the first optical waveguide from the first optical waveguide to the third optical waveguide, and 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 of embodiments 1, 2, 5, or 6 is characterized in that the incident light includes pulsed light resulting from crosstalk between the third optical waveguide and the first optical waveguide, the power of the emitted light emitted from 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 emitted light, which includes pulsed light resulting from crosstalk between the first optical waveguide and the third optical waveguide. 【0030】 In this case, as described in Embodiment 1, crosstalk occurs between the first optical waveguide and the second optical waveguide, and the emitted light, including pulsed light due to this crosstalk, is emitted from one end of the first optical waveguide. Furthermore, in this embodiment, the 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 that crosstalks from the first optical waveguide to the third optical waveguide is also pulsed and propagates from one end to the other of the third optical waveguide, generally running parallel to the incident light propagating through the first optical waveguide. The incident light that reaches the other end of the first optical waveguide is incident on the first connecting optical waveguide. The crosstalk light that reaches the other end of the third optical waveguide is incident on the second connecting optical waveguide. As described above, the propagation speed of incident light and the propagation speed of crosstalk light are equal to each other. Therefore, the incident light and the crosstalk light pass each other approximately at the midpoint of the optical waveguide, which is the first connecting optical waveguide, the second optical waveguide, and the second connecting optical waveguide combined. 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 of the incident light entering the third optical waveguide and the timing of the crosstalk light entering the first optical waveguide are approximately the same. For this reason, the crosstalk light propagates through the first optical waveguide from one end to the other, while generally running parallel to the incident light propagating through the third optical waveguide from one end to the other. During this time, incident light propagating through the third optical waveguide propagates while crosstalking with the first optical waveguide. Therefore, the light crosstalking from the third optical waveguide to the first optical waveguide combines with the crosstalk light propagating through the first optical waveguide. The combined light is pulsed, and the emitted light from one end of the first optical waveguide includes pulsed light generated by the crosstalk between the first optical waveguide and the third optical waveguide. The light emitted from the first optical waveguide is received by an OTDR, and the power of this emitted light is measured. 【0031】 At this time, pulsed light resulting from crosstalk between the first and second optical waveguides, and pulsed light resulting from crosstalk between the first and third optical waveguides, are emitted from one end of the first optical waveguide at different timings. Therefore, by receiving the emitted light containing the light from the crosstalk between the first and second optical waveguides, and the emitted light containing the light from the crosstalk between the first and third optical waveguides, with an OTDR, the power of each emitted light can be measured, and the magnitude of each crosstalk can be determined. Therefore, compared to the case in Embodiment 1, where the crosstalk between the first optical waveguide and the second optical waveguide is measured, and then the other end of the first optical waveguide and the other end of the third optical waveguide are optically connected with a connecting optical waveguide, and incident light is again 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 a 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 the light loss, reflectance, bending loss, and disconnection in the optical device. 【0033】 In this case, since the above measurements can be performed in parallel with the crosstalk measurement, the effort required for measurements other than crosstalk can be reduced. 【0034】 Aspect 12 of the present invention is a crosstalk measurement method according to any one of aspects 1 to 11, characterized in that when light of the same power is propagated in the first optical waveguide, the second optical waveguide, and the first connecting optical waveguide, the power of the backscattered light per unit length generated in the first connecting optical waveguide is smaller than the power of the backscattered light per unit length generated in the first optical waveguide and the second optical waveguide, respectively. 【0035】 In the first connecting optical waveguide, the low power of the backscattered light increases the ratio of the power of the crosstalk light to the power of the backscattered light, making it easier to detect the crosstalk light. 【0036】 Aspect 13 of the present invention is a crosstalk measuring device for an optical device having a first optical waveguide and a second optical waveguide that are arranged in parallel with each other and include one end and the other end, comprising: 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 measures the power of emitted light emitted from the one end of the first optical waveguide, which includes pulsed incident light incident from the one end of the first optical waveguide, and light generated by the crosstalk of the incident light from the first optical waveguide to the second optical waveguide, and light generated by the crosstalk of the incident light incident from the first optical waveguide to the second optical waveguide via the first connecting optical waveguide, and 【0037】 According to the crosstalk measurement device of this embodiment, since the light incident on one optical waveguide is crosstalked to another optical waveguide using an OTDR, the power of the crosstalked light is greater compared to the case where backscattered light of crosstalked light is detected as in Patent Documents 2 and 3. Furthermore, in the crosstalk measurement device of this embodiment, the crosstalk light when the incident light propagates from one end to the other of the first optical waveguide and the crosstalk light when the incident light propagates from the other end to the one end of the second optical waveguide are combined, so the power of the pulsed light generated by crosstalk tends to be large. Therefore, according to the crosstalk measurement device of this embodiment, crosstalk can be easily measured. 【0038】 As described above, the present invention provides a crosstalk measurement method and a crosstalk measurement apparatus that can easily measure crosstalk using the OTDR method. [Brief explanation of the drawing] 【0039】 [Figure 1] This figure shows a cross-section perpendicular to the longitudinal direction of a multicore fiber according to the first embodiment of the present invention. [Figure 2] This figure shows a crosstalk measuring device in the first embodiment. [Figure 3] This is a flowchart showing the procedure for the crosstalk measurement method in the first embodiment of the present invention. [Figure 4] This figure shows the propagation of light in a crosstalk measurement device. [Figure 5] This figure shows the measurement results from OTDR. [Figure 6] This is a magnified view of a portion of Figure 5. [Figure 7] This figure shows the power of crosstalk light measured by OTDR when the length of a multicore fiber is varied. [Figure 8] This figure shows the relationship between the crosstalk light power measured in the first embodiment and the crosstalk light power measured by the PM method. [Figure 9] This is a flowchart showing the procedure for the crosstalk measurement method in the second embodiment of the present invention. [Figure 10] This figure shows the crosstalk measuring device in the second measurement step of the second embodiment. [Figure 11] This figure shows a crosstalk measuring device according to a third embodiment of the present invention. [Figure 12] This figure shows the measurement results using OTDR in the third embodiment. [Figure 13] This figure shows a crosstalk measuring device according to a fourth embodiment of the present invention. [Figure 14] This figure shows a crosstalk measuring device according to a fifth embodiment of the present invention. [Figure 15] Figure 4 shows the measurement results from the OTDR when a hollow core optical fiber is used as the first optical fiber. [Figure 16]This figure shows a modified example of the crosstalk measuring device of the first embodiment. [Modes for carrying out the invention] 【0040】 The following examples illustrate embodiments for implementing the crosstalk measurement method and crosstalk measurement apparatus according to the present invention, with reference to the accompanying drawings. The embodiments illustrated below are provided to facilitate understanding of the present invention and are not intended to limit its interpretation. The present invention can be modified and improved from the following embodiments without departing from its spirit. Note that in the drawings referenced below, the dimensions of each component may be shown differently for the sake of clarity. 【0041】 (First Embodiment) Figure 1 shows a cross-section of the multicore fiber of this embodiment perpendicular to the longitudinal direction. The multicore fiber 10 has a plurality of cores 11 to 14 capable of transmitting light, and a cladding 15 surrounding the outer circumferential surface of each of the cores 11 to 14. The outer circumferential surface of the cladding 15 may be surrounded by a coating layer made of resin. 【0042】 Each of the cores 11-14 has one end and the other end, and they are arranged in parallel with each other along the longitudinal direction of the multicore fiber 10. The refractive index of the cores 11-14 is higher than that of the cladding 15, and each of the cores 11-14 is capable of transmitting light. For this reason, each of the cores 11-14 can be understood as a first optical waveguide to a fourth optical waveguide, and the multicore fiber 10 is an optical device having multiple optical waveguides arranged in parallel with each other. 【0043】 In this embodiment, cores 11-14 are made of silica glass to which a dopant that increases the refractive index, such as germanium (Ge), is added, and cladding 15 is made of silica glass without any additives. For example, cores 11-14 may be made of silica glass without any additives, and cladding 15 may be made of silica glass to which a dopant that decreases the refractive index, such as fluorine (F), or cores 11-14 may be made of silica glass to which a dopant that increases the refractive index is added, and cladding 15 may be made of silica glass to which a dopant that decreases the refractive index is added. Furthermore, the dopant that increases the refractive index and the dopant that decreases the refractive index are not particularly limited. 【0044】 Next, a crosstalk measurement device in the optical device of this embodiment will be described. Figure 2 is a diagram showing the crosstalk measurement device in this embodiment. As shown in Figure 2, the crosstalk measurement device 1 of this embodiment mainly comprises an OTDR 20, a processing unit 25, 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, one end 17 and the other end 18 may also be described as one end 17 and the other end 18 of cores 11 to 14. 【0045】 The OTDR20 is used in conjunction with optical fibers, etc., and emits pulsed light to measure the power of light incident from a multicore fiber 10, and the time from the emission of pulsed light until the incident light to be measured. It is a device that can measure optical losses such as transmission loss, bending loss, and connection loss in optical fibers, detect breaks in optical fibers, and measure the amount of light reflected. In this embodiment, a fan-in-fan-out device 30 is connected to the OTDR20. 【0046】 The fan-in / fan-out device 30 includes a plurality of optical waveguides (not shown) that can be individually optically connected to cores 11-14 at one end 17 of the multicore fiber 10, and optical fibers 31-34, each containing a core individually optically connected to the respective optical waveguide. In this example, the core of optical fiber 31 is connected to the OTDR 20. Also in this example, the optical waveguide connected to the core of optical fiber 31 is connected to core 11 of the multicore fiber 10. Therefore, optical fiber 31 and core 11 are optically connected, and light emitted from the OTDR 20 is incident on 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 similar configuration to the fan-in / fan-out device 30, and the cores of optical fibers 41 to 44 are individually optically connected to multiple optical waveguides (not shown) that can be individually optically connected to the cores 11 to 14 of the multicore fiber 10. In this example, core 11 is optically connected to the core of optical fiber 41, and core 12 is optically connected to the core of optical fiber 42. 【0048】 The first optical fiber 51 is a single-core fiber, for example, a single-mode fiber. One end of the first optical fiber 51 is connected to an optical fiber 41, and the other end of the first optical fiber 51 is connected to an optical fiber 42. Therefore, the core of optical fiber 41 and the core of 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 understood as a first connecting waveguide that optically connects the other end of the first optical waveguide, which is core 11, and the other end of the second optical waveguide, which is core 12. 【0049】 The OTDR20 is connected to the processing unit 25, and data related to the power of the light received by the OTDR20 is output to the processing unit 25. The processing unit 25 is a computing device that uses the light power measured by the OTDR20 to determine the magnitude of crosstalk. The processing unit 25 can use integrated circuits such as a microcontroller, IC (Integrated Circuit), LSI (Large-scale Integrated Circuit), ASIC (Application Specific Integrated Circuit), or NC (Numerical Control) device. Furthermore, if an NC device is used for the processing unit 25, it may or may not use a machine learning machine. When the processing unit 25 receives data related to the light power from the OTDR20, it uses this data to determine the magnitude of crosstalk between core 11 and core 12, as described later, and outputs data related to the determined magnitude of crosstalk. Note that the processing unit 25 and the OTDR20 may be housed in a single enclosure, and some components may be shared. 【0050】 Next, a crosstalk measurement method in the optical device of this embodiment will be described. Figure 3 is a flowchart showing the procedure of the crosstalk measurement method in this embodiment. As shown in Figure 3, the crosstalk measurement method of this embodiment comprises a 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 to be measured and set in the crosstalk measurement device 1. The length of the multicore fiber 10 is, for example, 21 km. In this step, the other end 18 of core 11 and the other end 18 of 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, and after this step, when light is incident from one end 17 of core 11, the light is incident from the other end 18 of core 12 via the core of the first optical fiber 51 into core 12. 【0052】 Furthermore, the OTDR20 and the core 11 are optically connected. Specifically, the 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. Thus, the light emitted from the OTDR20 enters the core 11 from one end 17. 【0053】 As shown in Figure 2, the core 11 of the multicore fiber 10 and the OTDR 20 are optically connected, and the core 11 and core 12 are optically connected via the core of the first optical fiber 51. 【0054】 (First measurement step S2) In this step, pulsed incident light emitted from the OTDR20 is introduced into the core 11, which is the first optical waveguide, from one end 17. The OTDR20 measures the power of the emitted light, which includes pulsed light resulting from the crosstalk between the incident light from the core 11 to the core 12, which is the second optical waveguide, and the crosstalk between the incident light entering the core 12 from the core 11 through the core of the first optical fiber 51, which is the first connecting optical waveguide, and the light resulting from the crosstalk between the core 12 and the core 11. 【0055】 Figure 4 shows the propagation of light in the crosstalk measurement apparatus shown in Figure 3. The above will be explained in detail using this figure. Note that in Figure 3, the fan-in-fan-out devices 30 and 40 are shown in a simplified manner. First, pulsed light is emitted from the OTDR 20. The wavelength width of this light is preferably 1 nm or more from the viewpoint of being able to stably perform the crosstalk measurement described later, more preferably 3 nm or more, and even more preferably 5 nm or more. Also, the wavelength width of this light is preferably 30 nm or less from the viewpoint of measuring crosstalk at a specific wavelength. Furthermore, the power of the light emitted from the OTDR 20 is preferably adjusted so as appropriate by adjusting the pulse width so that the emitted light, including the crosstalk light described later, does not saturate. In this case, an attenuator may be interposed between the OTDR 20 and the optical fiber 31. 【0056】 The pulsed light emitted from the OTDR20 enters the core 11 as incident light from one end 17 to the other end 18 of the core 11. The pulsed incident light propagating through the core 11 propagates from the core 11 to the core 12 while crosstalking. Because the incident light is pulsed, the crosstalk light CL1 that crosstalks from the core 11 to the core 12 is also pulsed and propagates from one end 17 to the other end 18 of the core 12, roughly parallel to the incident light L. During this time, because of the crosstalk from the core 11 to the core 12, the power of the incident light L decreases in proportion to the distance it propagates through the core 11, and the power of the crosstalk light CL1 increases in proportion to the distance it propagates through the core 12. Since the speed of light propagating through the core 11 and the core 12 is the same, the incident light L and the crosstalk light CL1 reach the other end 18 roughly simultaneously. 【0057】 Next, the incident light L and the crosstalk light CL1 enter the core of the first optical fiber 51 approximately simultaneously via the fan-in-fan-out device 40. At this time, the crosstalk light CL1 enters the core of the first optical fiber 51 from the side opposite to the side from which the incident light L enters. The incident light L and the crosstalk light CL1 entering the core of the first optical fiber 51 pass each other approximately at 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 approximately simultaneously. Then, via the fan-in-fan-out device 40, the incident light L enters the core 12 from the other end 18, and the crosstalk light CL1 enters the core 11 from the other end 18. At this time, the incident light L and the crosstalk light CL1 enter the cores 12 and 11, respectively, approximately simultaneously. Even if the lengths of the optical fibers 41 and 43 in the fan-in-fan-out device 40 are different, the incident light L and the crosstalk light CL1 are incident on the cores 12 and 11, respectively, approximately simultaneously. 【0058】 The incident light L that enters core 12 and the crosstalk light CL1 that enters core 11 propagate through cores 12 and 11 towards one end 17, generally in parallel. During this time, the incident light L propagating through core 12 also propagates through core 11 while crosstalking with it. Therefore, the light crosstalking from core 12 to core 11 combines with the crosstalk light CL1 propagating through core 11. The combined light is pulsed and propagates while gradually increasing in power. From one end 17 of core 11, the emitted light is a combination of the pulsed crosstalk light CL1 and light such as backscattered light. Therefore, the emitted light includes the pulsed crosstalk light CL1. 【0059】 The light emitted from the core 11 is incident on the OTDR20 via the fan-in-fan-out device 30, received by the OTDR20, and its power is measured by the OTDR20. 【0060】 Figure 5 shows the measurement results of the emitted light received by the OTDR20. In Figure 5, the horizontal axis represents the propagation distance of the incident light L, and the vertical axis represents the power of the emitted light received by the OTDR20. The vertical axis in Figure 5 shows the power of the emitted light in decibels as a ratio to a predetermined power set for the OTDR20. For example, if this predetermined power is 1 mW, the unit of the vertical axis may be shown in dBm. As shown in Figure 5, in the section where the incident light L propagates through core 11 and the section where the incident light L propagates through core 12, backscattered light is measured as emitted light. The slope of the line showing the emitted light in these sections indicates the loss of incident light L per unit length due to backscattering. In addition, pulsed light is measured at the boundary between the section of core 11 and the section of the first optical fiber 51, and at the boundary between the section of the first optical fiber 51 and the section of core 12. This light indicates reflection in the fan-in-fan-out device 40, etc. 【0061】 A 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 pass each other approximately at the midpoint of the first optical fiber 51, so this pulsed light represents the crosstalk light CL1. In addition, backscattered light is measured as emitted light in the section in which the incident light L propagates through the 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 shown above, a pulse indicating the power of the crosstalk light CL1 is shown approximately at the midpoint of the section representing 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 length of the core of the first optical fiber 51, which is the first connecting optical waveguide, be longer than the half-width of the incident light L. In other words, the length of the first optical fiber 51 should be L SCF Let ΔT be the half-width of the incident light L. pulseLet the refractive index of the core of the first optical fiber 51 be n, and when the speed of light is c, it is preferable to satisfy the following equation. L SCF >ΔT pulse ×c / n 【0063】 In addition, from the viewpoint of further suppressing the influence of the end portion of the first optical fiber 51 on the pulse, it is more preferable to satisfy the following equation. L SCF >1.2×ΔT pulse ×c / n 【0064】 OTDR 20 outputs data related to the measured power of the emitted light to the processing unit 25. 【0065】 (Processing step S3) In this step, the magnitude of the crosstalk between the core 11 and the core 12 is obtained using the measured power of the emitted light. FIG. 6 is an enlarged view of the emitted light measured at approximately the midpoint of the first optical fiber 51 in FIG. 5. As described above, backscattered light also occurs in the first optical fiber 51. Therefore, in the region other than the region where the pulsed light is shown, the power of this backscattered light is measured. Therefore, the processing unit 25 first calculates the power P of the backscattered light in the region where the pulsed light is shown from the power of the emitted light in the region other than the region where the pulsed light including the crosstalk light CL1 is shown, based on the data input from the OTDR 20. BS Specifically, the processing unit 25 approximates the power of the emitted light in the region other than the region where the pulsed light is shown, for example, by linear approximation, to obtain the power P of the backscattered light. BS Next, the processing unit 25 calculates the difference between the power P of the emitted light in the region where the pulsed light is shown and the obtained power P of the backscattered light. This difference becomes the power of the pulsed light. However, this power of the pulsed light includes the power P of the crosstalk light CL1 and the power P of the crosstalk in the fan-in / fan-out devices 30 and 40. OUT and the obtained power P of the backscattered light BS The power P of XT_MCF and the power P of the crosstalk in the fan-in / fan-out devices 30 and 40 XT_FIFO is included. The power P XT_FIFOIf the crosstalk is negligibly small, the power of the pulsed light is the power of the crosstalk light CL1 P XT-MCF This should be done. However, the power P from this pulsed light XT_FIFO The power with crosstalk removed is the power P of the CL1 optical fiber. XT_MCF Doing so will result in a more accurate power P XT_MCF From the perspective of seeking this, it is preferable. 【0066】 Power P XT_FIFO This can be measured in advance. For example, in the crosstalk measuring device 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 of the pulsed light P measured at approximately the midpoint of the first optical fiber 51 is OUT Power P XT_FIFO and Power P BS This includes. Therefore, in the same manner as above, Power P OUT and Power P BS By calculating the difference between this and Power P XT_FIFO It is possible to find this. 【0067】 The processing unit 25 calculates the power P of the crosstalk light CL1. XT_MCF The crosstalk magnitude is converted and output. At this time, the processing unit 25 may convert the crosstalk magnitude into decibels, which represent the ratio of the power of the incident light L emitted from one end 17 of the core 12, and output it. Alternatively, the processing unit 25 may convert it into decibels, which represent the ratio to a predetermined power defined in the OTDR20 shown in Figures 5 and 6, and output it. In this way, the crosstalk magnitude is determined. 【0068】 In this step, the processing unit 25 may further determine, for example, the magnitude of the crosstalk between core 11 and core 13 based on the determined magnitude of the crosstalk between core 11 and core 12. In this case, the processing unit 25 determines the magnitude of the crosstalk between core 11 and core 13 using, for example, a relational expression showing the relationship between the magnitude of the crosstalk between core 11 and core 12 and the magnitude of the crosstalk between core 11 and core 13, based on the magnitude of the crosstalk between core 11 and core 12. In this case, since the multicore fiber 10, which is an optical device, has a core 13, which is a third optical waveguide, in parallel with the core 11, which is a first optical waveguide, in processing step S3, the magnitude of the crosstalk between the first waveguide and the third waveguide will be further determined based on the determined magnitude of the crosstalk between the first waveguide and the second waveguide. In this case, the magnitude of the crosstalk between core 11 and core 13 can be easily determined without measuring the optical power due to the crosstalk between core 11 and core 13. Alternatively, the magnitude of the crosstalk between core 11 and core 14 may be determined in the same way as the magnitude of the crosstalk between core 11 and core 13. 【0069】 Next, the reliability of crosstalk measurement in this embodiment will be explained. 【0070】 Figure 7 shows the power of pulsed light consisting of crosstalk light CL1 in the multicore fiber 10 and crosstalk light in the fan-in-fan-out devices 30 and 40, measured by the OTDR20 in the same manner as in the above embodiment, with the power of backscattered light excluded from the power of light incident on the OTDR20. As shown in Figure 7, in this example, the lengths of the multicore fiber 10 were set to 0 km, 21 km, 42 km, and 84 km. The dotted line in Figure 7 shows a FIFO where the fan-in-fan-out device 30 and the fan-in-fan-out device 40 are directly connected, indicating that the length of the multicore fiber 10 is 0 km, and the power P XT_FIFO This corresponds to [the above]. As shown in Figure 7, it can be seen that the longer the multicore fiber 10, the greater the power of the light generated by crosstalk. 【0071】 Next, fan-in-fan-out devices 30 and 40 were connected to each of the multicore fibers 10 used in the measurement in Figure 7, and the magnitude of crosstalk was measured using the PM method. Specifically, light was incident from 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 magnitude of crosstalk between core 11 and core 12 was measured by measuring 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. 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 core 12. The results are shown in Table 1 below. TIFF0007873720000001.tif80170 【0072】 In Table 1, Peak Size is the power of the pulsed light shown in Figure 7, and Crosstalk is the magnitude of the crosstalk measured by the PM method. Figure 8 shows 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 Figure 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 Figure 8 is approximated by a straight line, the line is given by the following equation. XT = 2.57x - 58.9 R 2 =0.986 However, in this equation, XT represents the magnitude of crosstalk, x represents the power of the crosstalk light, and R 2 This is the coefficient of determination. As you can see, the coefficient of determination is quite close to 1, indicating a high correlation. 【0073】 Next, several other multicore fibers 10 were prepared, and the magnitude of the crosstalk was measured in the same manner as in this embodiment. In this case, 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 obtain the magnitude of the crosstalk shown in decibels on the vertical axis of Figure 8. In addition, the crosstalk of each multicore fiber 10 was measured using the PM method. The results are shown in Table 2. TIFF0007873720000002.tif68170 【0074】 In Table 2, XT calculation is the magnitude of crosstalk obtained using the linearly approximated formula described above, 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 were in general agreement. Therefore, in processing step S3, when the processing unit 25 converts the magnitude of crosstalk into decibels, which represent the ratio of the power of the incident light L output from one end 17 of the core 12, the magnitude of crosstalk XT may be obtained from the linearly approximated formula described above, with x being the power of the pulsed crosstalk light. 【0075】 The above demonstrates that the crosstalk measurement method of this embodiment is reliable. 【0076】 Next, the measurement of crosstalk in this embodiment will be explained using mathematical formulas. 【0077】 The length of the multicore fiber 10 is L MCF The length of the first optical fiber 51 is set to L SCF Let P0 be the power when the incident light L enters the core 11 of the multicore fiber 10 from one end 17, P'0 be the power when the incident light L exits from the other end 18, and P''0 be the power when the incident light L enters the core 12 from the other end 18 and exits from one end 17 of the core 12. Also, let P''0 be the power of the crosstalk light that exits from the core 12 due to crosstalk between the core 11 and the core 12 while the incident light L propagates through the core 11.XT (L MCF ) and while the incident light L propagates through core 11 and core 12, that is, while the incident light L travels back and forth through the multicore fiber 10, the power P of the crosstalk light emitted from core 11 crosstalks between core 11 and core 12. XT (2L MCF ) 【0078】 For simplicity, in the following explanation using mathematical formulas, the multicore fiber 10 will be described as a two-core fiber having cores 11 and 12, but not cores 13 and 14. Furthermore, the transmission loss of the multicore fiber 10 and the first optical fiber 51 will be ignored, as will the loss and crosstalk in the fan-in-fan-out devices 30 and 40. In this case, referring to equations (21a) and 21(b) of Non-Patent Literature 1, P'0, P''0, P XT (L MCF ), P XT (2L MCF ) is shown by the following equations (1) to (4). TIFF0007873720000003.tif12170TIFF0007873720000004.tif12170TIFF0007873720000005.tif12170TIFF0007873720000006.tif12170 【0079】 In the above equation, h is the power coupling coefficient between the crosstalking core 11 and core 12. The unit of optical power here is not expressed in decibels, but for example, in watts. 【0080】 Furthermore, the magnitude of the crosstalk from core 11 to core 12 during the propagation of incident light L through core 11 is expressed in decibels as a ratio to P'0, and this magnitude is called XT(L MCF Let XT(2L) be the magnitude of the crosstalk between core 11 and core 12, expressed in decibels as a ratio to P''0, while the incident light L propagates through core 11 and core 12, that is, while the incident light L travels back and forth through the multicore fiber 10. MCF ) In this case, XT(L MCF ), XT (2LMCF ) is shown by the following equations (5) and (6). TIFF0007873720000007.tif12170TIFF0007873720000008.tif12170 【0081】 As described above, the OTDR20 is optically connected to the core 11 at one end 17 of the multicore fiber 10. Therefore, the OTDR cannot measure P''0. Thus, XT(2L) is calculated from the optical power measured by the OTDR20. MCF To find ), we can use equation (6) as follows: 【0082】 As described above, the incident light L and the crosstalk light CL1 pass each other approximately at the midpoint of the first optical fiber 51. At this time, the distance the incident light L has propagated is equal to the length L of the multicore fiber 10. MCF and half the length of the first optical fiber 51 L SCF It is / 2. Therefore, the distance from the midpoint of the first optical fiber 51 to one end 17 of the multicore fiber 10 is L MCF +L SCF The result is / 2. The intensity of the backscattered light from the midpoint of the first optical fiber 51, measured by OTDR20, is P BS (L MCF +L SCF If we set it to / 2), then P BS (L MCF +L SCF / 2) is shown by equation (7). TIFF0007873720000009.tif12170 【0083】 In equation (7), α S_SCF This is the backscattering coefficient of the first optical fiber 51, indicating the probability that the incident light L will be Rayleigh scattered in the first optical fiber 51, and B SCF This indicates the probability that Rayleigh-scattered light propagates from the core of the first optical fiber 51 toward the core 11 of the multicore fiber 10, based on the capture rate of the first optical fiber 51. 【0084】 Equation (8) can be derived from equations (2) and (7). TIFF0007873720000010.tif12170 【0085】 By finding P''0 from equation (8) and substituting it into equation (6), we obtain equation (9). TIFF0007873720000011.tif36170 【0086】 As explained in processing step S3, P BS (L MCF +L SCF / 2) can be determined from the power of the emitted light in the region other than the region where pulsed crosstalk light is shown, based on the data input from OTDR20. Also, in this explanation, crosstalk in the fan-in-fan-out devices 30 and 40 is ignored, so the power P explained in processing step S3 is... XT_MCF P XT (2L MCF ) Therefore, P XT (2L MCF ) can be obtained as explained in processing step S3. Therefore, by separately calculating the first term of equation (9), XT(2L) can be obtained from equation (9). MCF ) can be determined. Note that the first term of equation (9) is the crosstalk magnitude determined in advance by the PM method and the P measured with OTDR20. BS (L MCF +L SCF / 2) and P XT (2L MCF It may also be determined from the relationship with ), or the first optical fiber 51 may be measured in advance to determine the first term of equation (9). 【0087】 As described above, the crosstalk measurement method of this embodiment comprises: a connection step S1 in which the other end 18 of the core 11, which is a first optical waveguide, and the other end 18 of the core 12, which is a second optical waveguide, are optically connected via the core of the first optical fiber 51, which is a first connecting optical waveguide; a first measurement step S2 in which pulsed incident light L emitted from the OTDR 20 is incident on one end 17 of the core 11, and the power of the emitted light CL1, which is a pulsed crosstalk light CL1 that is a combination of light generated by the crosstalk of the incident light L from the core 11 to the core 12 and light generated by the crosstalk of the incident light L incident on the core 11 to the core 12 via the core of the first optical fiber 51, and the power of the emitted light emitted from one end 17 of the core 11 is measured with the OTDR 20; and a processing step S3 in which the magnitude of the crosstalk between the core 11 and the core 12 is determined using the measured power of the emitted light. 【0088】 Furthermore, the crosstalk measuring device of this embodiment includes the core of a first optical fiber 51 that optically connects the other end 18 of core 11 and the other end 18 of core 12; an OTDR 20 that measures the power of the emitted light emitted from one end 17 of core 11, which includes pulsed crosstalk light CL1 formed by the crosstalk of pulsed incident light L from core 11 to core 12 when pulsed incident light L is incident from one end 17 of core 11, and light formed by the crosstalk of incident light L incident from core 11 to core 12 through the core of the first optical fiber 51 and the crosstalk of core 12 to core 11; and a processing unit 25 that determines the magnitude of the crosstalk between core 11 and core 12 using the measured power of the emitted light. 【0089】 According to this crosstalk measurement method and crosstalk measurement device, since the light incident on the core 11 using the OTDR20 is used to crosstalk with the core 12, the power of the crosstalk light is greater compared to the case where backscattered light of the crosstalked light is detected as in Patent Documents 2 and 3. Furthermore, in the crosstalk measurement method and crosstalk measurement device of this embodiment, the light that crosstalks when the incident light L propagates from one end 17 to the other end 18 of the core 11 and the light that crosstalks when the incident light L propagates from the other end 18 to the one end 17 of the core 12 are combined, so the power of the pulsed crosstalk light CL1 generated by the crosstalk tends to be large. Accordingly, according to the crosstalk measurement method and crosstalk measurement device of this embodiment, 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 identical or equivalent to those in the above embodiments are denoted by the same reference numerals unless otherwise specified, and redundant descriptions are omitted. 【0091】 Figure 9 is a flowchart showing the procedure for the crosstalk measurement method in this embodiment. As shown in Figure 9, the crosstalk measurement method in 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 in the crosstalk measurement method of the first embodiment. 【0092】 (Second measurement step S22) In this embodiment, this step is performed after the first measurement step S2. Figure 10 shows the crosstalk measurement apparatus in this step. As shown in Figure 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 the light emitted from the OTDR 20 is incident on the core 12 from one end 17. 【0093】 In this step, pulsed incident light emitted from the OTDR 20 is introduced into the core 12, which is the second optical waveguide, from one end 17. In this case, a multi-channel OTDR may be used, and in the first measurement step S2, light may be introduced into the core 11 from one channel of the OTDR 20, and in this step, light may be introduced into the core 12 from the other channel of the OTDR 20. In this step, the power of the incident light L introduced into the core 12 from the OTDR 20 is the same as the power of the incident light L introduced into the core 12 from the OTDR 20 in the first measurement step S2. The incident light L introduced into 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 introduced into the core 11 from the core 12 via the core of the first optical fiber 51, which is the first connecting optical waveguide. The incident light L introduced into the core 11 crosstalks from the core 11 to the core 12. In this way, the light generated by crosstalk from core 12 to core 11 and the light generated by crosstalk from core 11 to core 12 combine to produce pulsed crosstalk light CL2, which is emitted from one end 17 of core 12. 【0094】 The OTDR20 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 Figure 5. However, the descriptions of core 11 and core 12 in Figure 5 should be read interchangeably. 【0095】 (Processing step S3) In processing step S3 of this embodiment, first, the processing unit 25 inverts the distribution of light power measured in the second measurement step S22, specifically the range from core 12 to core 11, along the horizontal axis. Then, the processing unit 25 takes the arithmetic mean of the distribution of light power measured in the first measurement step S2, the range from core 11 to core 12, and the distribution of light power inverted in this step. By doing this, the power of light backscattered when propagating through core 11 from one end 17 to the other end 18, and the power of light backscattered when propagating through core 11 from the other end 18 to the first end 17 are averaged out, and the slope of the distribution of light power in the range of core 11 in Figure 5 is almost eliminated. Similarly, the slope of the distribution of light power showing the range of core 12 in Figure 5, and the slope of the distribution of light power in the range of the first optical fiber 51 are almost eliminated. Furthermore, approximately at the midpoint of the first optical fiber 51, a pulsed crosstalk light appears, which is an average of the crosstalk light CL1 and the crosstalk light CL2. 【0096】 Next, in this step, the processing unit 25 determines the magnitude of the crosstalk light from the power of the averaged pulsed crosstalk light in the same manner as in the first embodiment. 【0097】 As described above, the crosstalk measurement method of this embodiment includes, in addition to the crosstalk measurement method of the first embodiment, a second measurement step S22 in which pulsed incident light L emitted from the OTDR 20 is incident on one end 17 of the core 12, and the power of the emitted light emitted from one end 17 of the core 12 is measured with the OTDR 20, which includes pulsed light generated when the incident light L crosstalks from the core 12 to the core 11 and when the incident light L incident on the first optical fiber 51 from the core 12 to the core 11 crosstalks from the core 11 to the core 12, and in the processing step S3, the magnitude of the crosstalk between the core 11 and the core 12 is determined using the power of the emitted light measured in the first measurement step S2 and the power of the emitted light measured in the second measurement step S22. 【0098】 Furthermore, the crosstalk measuring device of this embodiment, in addition to the crosstalk measuring device of the first embodiment, includes a pulsed light OTDR 20 which includes pulsed incident light L incident from one end 17 of the core 12, light generated by the crosstalk of the incident light L from the core 12 to the core 11, and light generated by the crosstalk of the incident light L incident from the core 12 to the core 11 through the core of the first optical fiber 51, and the output light emitted from the core 11 to the core 12. The OTDR 20 measures the power of the output light emitted from one end 17 of the core 12, and the processing unit 25 uses the power of the output light emitted from one end 17 of the core 11 due to the incident light L incident from the core 11, and the power of the output light emitted from one end 17 of the core 12 due to the incident light L incident from the core 12 to determine the magnitude of the crosstalk between the core 11 and the core 12. 【0099】 According to the crosstalk measurement method and crosstalk measurement apparatus of this embodiment, since it uses 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, the magnitude of the crosstalk can be determined more accurately compared to the case where 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 core 11 in the first measurement step S2 and the power of the incident light L incident on core 12 in the second measurement step S22 are equal, and in processing step S3, the magnitude of the crosstalk between core 11 and core 12 is determined using the result of averaging the power of the emitted light measured in the first measurement step S2 and the power of the emitted light measured in the second measurement step S22. By using such averaging processing, the magnitude of the crosstalk can be easily and accurately determined. Note that the power of the incident light L incident on core 11 in the first measurement step S2 and the power of the incident light L incident on core 12 in the second measurement step S22 may be different. In this case, in processing step S3, the power of the incident light L is taken into account when processing. 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 identical or equivalent to those in the above embodiments are denoted by the same reference numerals unless otherwise specified, and redundant descriptions are omitted. 【0102】 Figure 11 shows a crosstalk measurement device 1 in this embodiment. The crosstalk measurement device 1 in this embodiment differs from the crosstalk measurement device 1 of the first embodiment in that the optical fiber 41 of the fan-in-fan-out device 40 is connected to one end of the first optical fiber 51 and the second optical fiber 52 via a coupler 55, 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. The optical waveguide connected to the core of the optical fiber 43 is connected to the 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 core 11 and core 12, similar to the first optical fiber 51 in the first embodiment, and the core of the second optical fiber 52 optically connects core 11 and core 13. The core of the second optical fiber can be understood as 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】 In this embodiment, the multicore fiber 10, which is an optical device, further has a third optical waveguide in parallel with the first optical waveguide, which is the core 11. In addition, 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 of a different length from the first connecting optical waveguide. 【0104】 The procedure for the crosstalk measurement method in this embodiment, using such a crosstalk measuring device 1, is the same as the flowchart shown in Figure 3. However, each step differs as follows. The differences are mainly explained below. 【0105】 (Connection step S1) In this step of the embodiment, the first optical fiber 51 and the second optical fiber 52 are connected to the optical fiber 41 via a coupler 55, and the end of the second optical fiber 52 opposite to the coupler 55 is connected to the optical fiber 43. In other words, in this embodiment, in addition to the connection step S1 of the first embodiment, the other end 18 of core 11 and the other end 18 of core 13 are optically connected via the core of the second optical fiber, which has a different length from the first optical fiber 51. In this way, core 11 and core 12 are optically connected, and core 11 and core 13 are optically connected. 【0106】 (First measurement step S2) In this step of the embodiment, incident light L is incident on the core 11 from the OTDR 20 in the same manner as in the first embodiment. 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 explained below. 【0107】 The incident light L entering core 11 from OTDR20 propagates through core 11 from one end 17 to the other end 18, crosstalking from core 11 to core 12 and from core 11 to core 13. The light crosstalking from core 11 to core 13 is also pulsed and propagates from one end 17 to the other end 18 of core 13, roughly parallel to the incident light L. The power of this crosstalk light CL2 increases with the distance it propagates through core 13. The crosstalk light CL2 enters the second optical fiber 52 from optical fiber 43 at roughly the same time that the incident light L enters the second optical fiber 52 from coupler 55. The incident light L and the crosstalk light CL2 pass each other at approximately the midpoint of the second optical fiber 52. Then, via the fan-in-fan-out device 40, at the other end 18 of the multicore fiber 10, the incident light L enters the core 13, and the crosstalk light CL2 enters the core 11 at approximately the same time as the incident light L enters the core 13. The incident light L that enters the core 13 and the crosstalk light CL2 that enters the core 11 propagate toward the end 17 of the respective cores 13 and 11, generally in parallel. During this time, the incident light L propagating through the core 13 also propagates through the core 11 while crosstalking with it. Therefore, the light crosstalking from the core 13 to the core 11 combines with the crosstalk light CL2 propagating through the core 11. The combined light is pulsed and propagates while gradually increasing in power. From the end 17 of the core 11, the emitted light is formed by combining the pulsed crosstalk light CL2 with light such as backscattered light. Therefore, the emitted light includes the pulsed crosstalk light CL2. The light emitted from the core 11 is incident on the OTDR20 via the fan-in-fan-out device 30, received by the OTDR20, and its power is measured by the OTDR20. 【0108】 Figure 12 shows the measurement results at the OTDR in this embodiment. Since the lengths of the first optical fiber 51 and the second optical fiber 52 are different, as shown in Figure 12, the emitted light including crosstalk light CL1 and the emitted light including crosstalk light CL2 are incident on the OTDR 20 at different timings. In this embodiment, since the second optical fiber 52 is longer than the first optical fiber 51, the emitted light including crosstalk light CL2 is incident on the OTDR at a later timing than the emitted light including crosstalk light CL1. Therefore, the OTDR 20 can measure each of these emitted lights. For this reason, the OTDR 20 measures the power of the emitted light, including pulsed light, twice. 【0109】 Furthermore, 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 greater than the half-width of the incident light. In this case, interference between pulsed light due to crosstalk between core 11 and core 12 and pulsed light due to crosstalk between core 11 and core 13 can be suppressed, and the magnitude of the crosstalk can be measured more accurately. 【0110】 (Processing step S3) In this step, the processing unit 25 uses the measured power of the emitted light to determine the magnitude of the crosstalk between core 11 and core 12, in the same manner as in the first embodiment. Furthermore, in this step of the embodiment, the processing unit 25 determines the magnitude of the crosstalk between core 11 and core 13. Since backscattered light is also generated in the first optical fiber 51 and the second optical fiber 52, the power of this backscattered light is measured in regions other than the region in which pulsed light including 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 region in which pulsed light including crosstalk light CL2 is shown from the power of the emitted light in regions other than the region in which pulsed light including crosstalk light CL2 is shown. Specifically, in the first embodiment, the processing unit 25 determines the power of the backscattered light P BSIn the same manner as when the crosstalk light CL2 was determined, the power of the backscattered light in the emitted light including the crosstalk light CL2 is determined. Next, the processing unit 25 determines the difference between the power of the emitted light in the region where pulsed light including the crosstalk light CL2 is shown and the power of the backscattered light determined. This difference is the power of the crosstalk light CL2. In this embodiment as well, the crosstalk power P in the fan-in-fan-out devices 30, 40 is also determined. XT_FIFO If the power is so small that it can be ignored, then that power may be ignored. However, the power P of the pulsed light obtained can be ignored. XT_FIFO From the viewpoint of more accurately determining the power P of the crosstalk optical fiber CL2, it is preferable to use the power remaining after removing the crosstalk optical fiber CL2 as the power of the crosstalk optical fiber CL2. 【0111】 The processing unit 25 converts the power of the crosstalk light CL1, obtained in the same manner as in the first embodiment, into the magnitude of the crosstalk and outputs it, and also converts the power of the obtained crosstalk light CL2 into the magnitude of the crosstalk and outputs it. At this time, the processing unit 25 may convert the magnitude of the crosstalk light CL2 into decibels, which represent the ratio of the power of the incident light L emitted from one end 17 of the core 13, and output it. Alternatively, the processing unit 25 may convert it into decibels, which represent the ratio to a predetermined power defined in OTDR20, and output it. In this way, the magnitude of the crosstalk between core 11 and core 12, as well as the magnitude of the crosstalk between core 11 and core 13, can be determined. 【0112】 In the crosstalk measurement method of this embodiment, in addition to the crosstalk measurement method of the first embodiment, in connection step S1, the other end 18 of core 11 and the other end 18 of core 13 are further optically connected via the core of a second optical fiber 52 having a different length from the core of the first optical fiber 51. In the first measurement step S2, the power of the emitted light emitted from one end 17 of core 11, which includes pulsed light generated by the crosstalk of incident light L from core 11 to core 13 and the crosstalk of incident light L entering core 11 from core 13 via the core of the second optical fiber 52 from core 13 to core 11, is further measured with an OTDR 20. In processing step S3, the magnitude of the crosstalk between core 11 and core 13 is further determined using the power of the emitted light, which includes pulsed crosstalk light CL2 generated by the crosstalk between core 11 and core 13. 【0113】 Furthermore, the crosstalk measuring device 1 of this embodiment further includes, in addition to the crosstalk measuring device 1 of the first embodiment, a core of a second optical fiber 52 having a different length from the core of a first optical fiber 51 that optically connects the other end 18 of core 11 and the other end 18 of core 13. The OTDR 20 includes pulsed light resulting from the crosstalk of incident light L from core 11 to core 13 and the crosstalk of incident light L that enters core 11 to core 13 via the core of the second optical fiber 52 from core 11 to core 11, and further measures the power of the emitted light emitted from one end 17 of core 11. The processing unit 25 further determines the magnitude of the crosstalk between core 11 and core 13 using the power of the emitted light, which includes pulsed crosstalk light CL2 generated by the crosstalk between core 11 and core 13. 【0114】 According to the crosstalk measurement method and crosstalk measurement apparatus 1 of this embodiment, the emitted light containing crosstalk light between core 11 and core 12, and the emitted light containing crosstalk light between core 11 and core 13 are received by the OTDR 20, the power of each emitted light can be measured, and the magnitude of each crosstalk can be determined. Therefore, compared to the first embodiment, where the magnitude of crosstalk between core 11 and core 12 is measured, and then core 11 and core 13 are optically connected with a connecting optical waveguide, and incident light is again 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 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 Figure 13. Note that components identical or equivalent to those in the above embodiments are denoted by the same reference numerals unless otherwise specified, and redundant descriptions are omitted. 【0117】 Figure 13 is a diagram illustrating the crosstalk measurement device in this embodiment, following Figure 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 or the same. 【0118】 The procedure for the crosstalk measurement method in this embodiment, using such a crosstalk measuring device 1, is the same as the flowchart shown in Figure 3. However, each step differs as follows. The differences are mainly explained below. 【0119】 (Connection step S1) In this step of the embodiment, in addition to the connection step S1 of the first embodiment, one end 17 of core 12 and one end 17 of 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, core 12 and core 13 are optically connected. 【0120】 (First measurement step S2) In this step of the embodiment, incident light L is incident on the core 11 from the OTDR 20 in the same manner as in the first embodiment. 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 explained below. 【0121】 The incident light L that enters core 11 from OTDR20 propagates through core 11 from one end 17 to the other end 18, and then enters core 12 via the first optical fiber 51. The incident light L that propagates through core 12 from the other end 18 to the one end 17 crosstalks from core 12 to core 11 and also crosstalks from core 12 to core 13, as described in the first embodiment. The light that crosstalks from core 12 to core 13 is also pulsed and propagates from the other end 18 to the one end 17 of core 13, generally running parallel to the incident light L. The power of this crosstalk light CL2 increases with the distance it propagates through core 13. The incident light L enters core 13 from core 12 via the second optical fiber 52, and the crosstalk light CL2 enters core 12 from core 13 via the second optical fiber 52. The incident light L and the crosstalk light CL2 pass each other approximately at the midpoint of the second optical fiber 52. Therefore, the timing of the incident light L entering core 13 and the timing of the crosstalk light CL2 entering core 12 are approximately the same. The incident light L entering core 13 and the crosstalk light CL2 entering core 12 propagate from one end 17 to the other end 18 of each core 13 and 12, generally in parallel. During this time, the incident light L propagating through core 13 also propagates through core 12 while crosstalking with it. Consequently, the light crosstalking from core 13 to core 12 combines with the crosstalk light CL2 propagating through core 12. The combined light is pulsed and propagates while gradually increasing in power. This pulsed light containing the crosstalk light CL2 enters core 11 from core 12 via the first optical fiber 51, and from one end 17 of core 11, the emitted light is a combination of the crosstalk light CL2 and light such as backscattered light. Therefore, the emitted light contains pulsed crosstalk light CL2. The light emitted from core 11 enters OTDR20, is received by OTDR20, and its power is measured by OTDR20. 【0122】 The timing at which the emitted light containing crosstalk light CL2 enters the OTDR20 is delayed by the time it takes for the light to propagate through the second optical fiber 52, core 12, first optical fiber 51, and core 11, compared to the timing at which the emitted light containing crosstalk light CL1 enters the OTDR20. Therefore, the OTDR20 can measure each of these emitted lights. For this reason, the OTDR20 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 the crosstalk between core 11 and core 12 in the same manner as in the first embodiment. Furthermore, in this step of the embodiment, the processing unit 25 determines the magnitude of the crosstalk between core 12 and core 13. The method for determining the crosstalk between core 12 and core 13 is the same as the method for determining the crosstalk between core 11 and core 13 in the third embodiment. 【0124】 The processing unit 25 converts the power of the crosstalk light CL1, obtained in the same manner as in the first embodiment, into the magnitude of the crosstalk and outputs it, and also converts the power of the obtained crosstalk light CL2 into the magnitude of the crosstalk and outputs it. At this time, the processing unit 25 may convert the magnitude of the crosstalk into decibels, which represent the ratio of the power of the incident light L emitted from the other end 18 of the core 13, and output it. Alternatively, the processing unit 25 may convert it into decibels, which represent the ratio to a predetermined power defined in OTDR20, and output it. In this way, the magnitude of the crosstalk between core 11 and core 12, as well as the magnitude of the crosstalk between core 11 and core 13, can be determined. 【0125】 In the crosstalk measurement method of this embodiment, in addition to the crosstalk measurement method of the first embodiment, in connection step S1, one end 17 of core 12 and one end 17 of core 13 are further optically connected via the core of the second optical fiber 52. In the first measurement step S2, the power of the emitted light, which includes pulsed light generated by the crosstalk of incident light L from core 12 to core 13 and the crosstalk of incident light L entering core 12 to core 13 via the core of the second optical fiber 52 and emitting from one end 17 of core 11 via the first optical fiber 51 and core 11, is further measured with the OTDR 20. In processing step S3, the magnitude of the crosstalk between core 12 and core 13 is further determined using the power of the emitted light, which includes pulsed crosstalk light CL2 generated by the crosstalk between core 12 and core 13. 【0126】 Furthermore, the crosstalk measuring device 1 of this embodiment further includes, in addition to the crosstalk measuring device 1 of the first embodiment, the core of a second optical fiber 52 that optically connects one end 17 of core 12 and one end 17 of core 13. The OTDR 20 includes pulsed light that is a combination of light generated by the crosstalk of incident light L from core 12 to core 13 and light generated by the crosstalk of incident light L that enters core 12 to core 13 via the core of the second optical fiber 52 and then crosstalks from core 13 to core 12. The processing unit 25 further measures the power of the emitted light that is emitted from one end 17 of core 11 via the first optical fiber 51 and core 11. The processing unit 25 further determines the magnitude of the crosstalk between core 12 and core 13 using the power of the emitted light, which includes pulsed crosstalk light CL2 generated by the crosstalk between core 12 and core 13. 【0127】 According to the crosstalk measurement method and crosstalk measurement apparatus 1 of this embodiment, the emitted light containing crosstalk light between core 11 and core 12, and the emitted light containing crosstalk light between core 12 and core 13 are received by the OTDR 20, the power of each emitted light can be measured, and the magnitude of each crosstalk can be determined. Therefore, compared to the first embodiment, where the magnitude of crosstalk between core 11 and core 12 is measured, and then core 12 and core 13 are optically connected with a connecting optical waveguide, and incident light is again 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 be easily measured. 【0128】 In this embodiment, as shown in Figure 9, a second measurement step S22 may be included after the first measurement step S2. In this case, in the second measurement step S22, pulsed incident light L emitted from the OTDR 20 is incident on the other end 18 of the core 13. The OTDR 20 includes pulsed light that is a combination of light generated by the crosstalk of the incident light L from the core 13 to the core 12 and light generated by the crosstalk of the incident light L, which is incident on the core 13 to the core 12 via the second optical fiber 52, from the core 12 to the core 13, and measures the power of the emitted light emitted from the other end 18 of the core 13. Furthermore, the OTDR20 includes pulsed light resulting from the crosstalk between core 12 and core 11 as the incident light L propagates from one end 17 to the other end 18 of core 12, and the crosstalk between core 11 and core 12 of the incident light L that enters core 11 via the first optical fiber 51. The power of the emitted light emitted from the other end 18 of core 13, via the second optical fiber 52 and core 13, is measured. In this processing step S3, the magnitude of the crosstalk between core 12 and core 13 is determined using the power of the emitted light measured in the first measurement step S2 and the power of the emitted light measured in the second measurement step S22, similar to the second embodiment. 【0129】 (Fifth embodiment) Next, a fourth embodiment of the present invention will be described in detail with reference to Figure 14. Note that components identical or equivalent to those in the above embodiments are denoted by the same reference numerals unless otherwise specified, and redundant descriptions are omitted. 【0130】 Figure 14 is a diagram illustrating the crosstalk measurement device in this embodiment, following Figure 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 connecting 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 or the same. 【0131】 The procedure for the crosstalk measurement method in this embodiment, using such a crosstalk measuring device 1, is the same as the flowchart shown in Figure 3. However, each step differs as follows. The differences are mainly explained below. 【0132】 (Connection step S1) In this step of the embodiment, in addition to the connection step S1 of the first embodiment, one end 17 of core 12 and the other end 18 of 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, core 12 and core 13 are optically connected. 【0133】 (First measurement step S2) In this step of the embodiment, incident light L is incident on the core 11 from the OTDR 20 in the same manner as in the first embodiment. 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 explained below. 【0134】 The incident light L entering core 11 from OTDR20 propagates through core 11 from one end 17 to the other end 18, crosstalking from core 11 to core 12, and also crosstalking from core 11 to core 13. The light crosstalking from core 11 to core 13 is also pulsed and propagates from one end 17 to the other end 18 of core 13, roughly parallel to the incident light L. The power of this crosstalk light CL2 increases with the distance it propagates through core 13. The incident light L and the crosstalk light CL2 arrive at the other end 18 at roughly the same time. The incident light L enters core 13 from the other end 18 of core 11, through the first optical fiber 51, core 12, and the second optical fiber 52, and then enters core 13 from the other end 18 of core 13. Furthermore, the crosstalk light CL2 enters core 11 from the other end 18 of core 13, via the second optical fiber 52, core 12, and first optical fiber 51. The incident light L and the crosstalk light CL2 pass each other approximately at the midpoint of the waveguide formed by the core of the first optical fiber 51, core 12, and the core of the second optical fiber 52. Therefore, the timing of the incident light L entering core 13 and the timing of the crosstalk light CL2 entering core 11 are approximately the same. The incident light L that entered core 13 and the crosstalk light CL2 that entered core 11 propagate through their respective cores 13 and 11 from the other end 18 to the one end 17, generally in parallel. During this time, the incident light L propagating through core 13 also propagates through core 11 while crosstalking with it. Consequently, the light crosstalking from core 13 to core 11 combines with the crosstalk light CL2 propagating through core 11. The combined light is pulsed and propagates while gradually increasing in power. From one end 17 of the core 11, emitted light is produced by combining this pulsed crosstalk light CL2 with light such as backscattered light. Therefore, the emitted light includes pulsed crosstalk light CL2. The emitted light from the core 11 is incident on the OTDR 20, received by the OTDR 20, and its power is measured by the OTDR 20. 【0135】 The timing at which the emitted light containing crosstalk light CL2 enters the OTDR20 is delayed by the time it takes for the light to propagate through the second optical fiber 52 and core 13 compared to the timing at which the emitted light containing crosstalk light CL1 enters the OTDR20. Therefore, the OTDR20 can measure each of these emitted lights. For this reason, the OTDR20 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 the crosstalk between core 11 and core 12 in the same manner as in the first embodiment. Furthermore, in this step of the embodiment, the processing unit 25 determines the magnitude of the crosstalk between core 11 and core 13. The method for determining the crosstalk between core 11 and core 13 is the same as the method for determining the crosstalk between core 11 and core 13 in the third embodiment. 【0137】 The processing unit 25 converts the power of the crosstalk light CL1, obtained in the same manner as in the first embodiment, into the magnitude of the crosstalk and outputs it, and also converts the power of the obtained crosstalk light CL2 into the magnitude of the crosstalk and outputs it. At this time, the processing unit 25 may convert the magnitude of the crosstalk into decibels, which represent the ratio of the power of the incident light L emitted from one end 17 of the core 13, and output it. Alternatively, the processing unit 25 may convert it into decibels, which represent the ratio to a predetermined power defined in OTDR20, and output it. In this way, the magnitude of the crosstalk between core 11 and core 12, as well as the magnitude of the crosstalk between core 11 and core 13, can be determined. 【0138】 In the crosstalk measurement method of this embodiment, in addition to the crosstalk measurement method of the first embodiment, in connection step S1, one end 17 of core 12 and the other end 18 of core 13 are further optically connected via the core of the second optical fiber 52. In the first measurement step S2, the power of the emitted light emitted from one end 17 of core 11, which includes pulsed light generated by the crosstalk of incident light L from core 11 to core 13 and the crosstalk of incident light L entering core 11 from core 13 via the cores of core 12 and the second optical fiber 52, is further measured with OTDR20. In processing step S3, the magnitude of the crosstalk between core 11 and core 13 is further determined using the power of the emitted light, which includes pulsed crosstalk light CL2 generated by the crosstalk between core 11 and core 13. 【0139】 Furthermore, the crosstalk measuring device 1 of this embodiment further includes, in addition to the crosstalk measuring device 1 of the first embodiment, the 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. The OTDR 20 includes pulsed light that is a combination of light generated by the crosstalk of incident light L from core 11 to core 13 and light generated by the crosstalk of incident light L that enters core 11 to core 13 through the cores of core 12 and the second optical fiber 52 from core 13 to core 11. The processing unit 25 further measures the power of the emitted light emitted from one end 17 of core 11, and the processing unit 25 further determines the magnitude of the crosstalk between core 11 and core 13 using the power of the emitted light, which includes pulsed crosstalk light CL2 generated by the crosstalk between core 11 and core 13. 【0140】 According to the crosstalk measurement method and crosstalk measurement apparatus 1 of this embodiment, the emitted light containing crosstalk light between core 11 and core 12, and the emitted light containing crosstalk light between core 11 and core 13 are received by the OTDR 20, the power of each emitted light can be measured, and the magnitude of each crosstalk can be determined. Therefore, compared to the first embodiment, where the magnitude of crosstalk between core 11 and core 12 is measured, and then core 11 and core 13 are optically connected with a connecting optical waveguide, and incident light is again 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 be easily measured. 【0141】 In this embodiment, as shown in Figure 9, a second measurement step S22 may be included after the first measurement step S2. In this case, in the second measurement step S22, pulsed incident light L emitted from the OTDR 20 is incident on one end 17 of the core 13. The OTDR 20 includes pulsed light obtained by the crosstalk of the incident light L from the core 13 to the core 11, and the crosstalk of the incident light L, which is incident on the core 13 to the core 11 via the second optical fiber 52, the core 12, and the first optical fiber 51, from the core 11 to the core 13, and measures the power of the emitted light emitted from one end 17 of the core 13. Furthermore, OTDR20 includes pulsed light resulting from the crosstalk between core 12 and core 11 as the incident light L propagates through core 12 from one end 17 to the other end 18, and the crosstalk between core 11 and core 12 of the incident light L incident on core 11 via the first optical fiber 51. The power of the emitted light emitted from one end 17 of core 13 is measured, via the second optical fiber 52 and core 13 from one end 17 of core 12. In this processing step S3, the magnitude of the crosstalk between core 11 and core 13 is determined using the power of the emitted light measured in the first measurement step S2 and the power of the emitted light measured in the second measurement step S22, similar to the second embodiment. 【0142】 Although the present invention has been described above with reference to the above embodiments, the present invention is not limited to these. 【0143】 For example, the arrangement and number of cores in the multicore fiber 10 may differ from those in the above embodiment. 【0144】 Furthermore, although the above embodiment described a multicore fiber as an example of an optical device with waveguides arranged in parallel, the optical device of the present invention is not limited to a multicore fiber. For example, it can be applied to optical fiber cables in which multiple optical fibers are arranged in a sequence, optical fiber tapes in which multiple optical fibers are arranged in a planar configuration, multi-element fibers in which multiple bare optical fibers are arranged within a single coating layer, and 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 OTDR20 may be used to further measure at least one of the optical loss, reflectance, bending loss, and breakage in an optical device such as a multicore fiber 10. 【0146】 Furthermore, the form of the fan-in-fan-out devices 30 and 40 is not particularly limited. Also, the crosstalk measuring device 1 does not need to include at least one of the fan-in-fan-out devices 30 and 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. Also, at least one of the first optical fiber 51 and the second optical fiber 52 may consist of a connector of multiple optical fibers. 【0147】 In the above embodiment, for example, as shown in Figure 5, the slope of the power of the backscattered light measured by the OTDR20 is approximately the same in sections such as core 11, 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 core 11, core 12, and the first optical fiber 51. Therefore, in the above embodiment, when light of the same power is propagated through core 11, 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 core 11, 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 core 11 and core 12, respectively. As an example of such a first optical fiber 51, a hollow-core optical fiber in which the core is hollow can be mentioned. Alternatively, the first optical fiber 51 may be an optical fiber in which the specific refractive index difference of the core of the first optical fiber 51 is smaller than that of the light propagating through the core of the multicore fiber 10, and the effective cross-sectional area of ​​the propagating light is larger. This is because the power of backscattered light is proportional to the numerical aperture (NA) corresponding to the specific refractive index difference. Figure 15 is a schematic diagram showing the measurement results on the OTDR 20 when a hollow-core optical fiber is used as the first optical fiber 51 in Figure 4. However, Figure 15 is a schematic diagram of the measurement results when a 2-core multicore fiber is used. As shown in Figure 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 becomes larger, making it easier to detect crosstalk light. For the same reasons as above, it is preferable that the power of backscattered light per unit length generated in the second optical fiber 52 of the third to fifth embodiments is smaller than the power of backscattered light per unit length generated in each of the cores 11 to 13. 【0148】 Furthermore, in the first embodiment, as shown in Figures 2 and 4, the cores 13 and 14 were described in an example where they were not connected to each other by optical fibers. However, the present invention is not limited to this. Figure 16 shows a modified example of the crosstalk measuring device of the first embodiment. As shown in Figure 16, this modified example differs from the first embodiment in that the optical fibers 43 and 44 of the fan-in-fan-out device 40 are connected to the second optical fiber 52, and the other end 18 of core 13 and the other end 18 of 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 the length of the first optical fiber 51. Therefore, the distance over which light propagates from the other end 18 of core 13 to the other end 18 of core 14 is the same as the distance over which light propagates from the other end 18 of core 11 to the other end 18 of core 12. In the first embodiment, pulsed light was measured, which was the result of a combination of crosstalk light CL1, where incident light crosstalks from core 11 to core 12, and crosstalk light CL1, where incident light crosstalks from core 12 to core 11. However, the crosstalk light CL1 that crosstalks from core 11 to core 12 also includes light that crosstalks from core 11 to cores 13 and 14, and then further 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 further crosstalks to core 11. In the first embodiment, since there is no optical connection between core 13 and core 14, the light that crosstalks from core 11 to cores 13 and 14 but does not further crosstalk to core 12 is emitted from the other end 18. However, according to this modified example, of the light that crosstalks from core 11 to core 13, the light that does not further crosstalk to core 12 is incident on 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 is incident on core 13 via the second optical fiber 52. When the light incident on cores 13 and 14 via the second optical fiber 52 propagates through cores 13 and 14 from the other end 18 to the one end 17, it further crosstalks with core 12.Furthermore, as described above, the distance over which light propagates from the other end 18 of core 13 to the other end 18 of core 14 is the same as the distance over which light propagates from the other end 18 of core 11 to the other end 18 of core 12. 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 has crosstalked from core 11 to cores 13 and 14 and 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 in the crosstalk light CL1 in both the forward and return paths. Therefore, in this modified example, the other ends 18 of the third waveguide core 13 and the fourth waveguide core 14, which crosstalk with the first waveguide core 11 and the second waveguide core 12 respectively, are optically connected via the core of the second connecting optical waveguide, the second optical fiber 52. Compared to the first embodiment, the magnitude of the crosstalk can be measured more accurately. 【0149】 As described above, the present invention provides a crosstalk measurement method and a crosstalk measurement apparatus that can easily measure crosstalk using the OTDR method, and is expected to be used in fields such as optical fiber communication.

Claims

[Claim 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, including one end and the other end, A connection 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 measurement step involves measuring the power of the emitted light emitted from the first end of the first optical waveguide using the OTDR, which includes pulsed incident light emitted from an OTDR (Optical Time Domain Reflectometer) and incident light generated by crosstalk between the first optical waveguide and the second optical waveguide via the first connecting optical waveguide, and the emitted light being crosstalk between the second optical waveguide and the first optical waveguide. A processing step of determining the magnitude of crosstalk between the first optical waveguide and the second optical waveguide using the measured power of the emitted light, Equipped with A crosstalk measurement method characterized by the following features. [Claim 2] The length of the first connecting optical waveguide is longer than the distance width of the incident light, which corresponds to the half-maximum time width of the incident light. The crosstalk measurement method according to feature 1. [Claim 3] The second measurement step further comprises measuring the power of the emitted light emitted from the first end of the second optical waveguide using the OTDR, wherein pulsed incident light emitted from the OTDR is incident from one end of the second optical waveguide, and the pulsed light is obtained by the crosstalk of the incident light from the second optical waveguide to the first optical waveguide and the crosstalk of the incident light incident light from the second optical waveguide to the first optical waveguide via the first connecting optical waveguide. In the processing step, the magnitude of the crosstalk between the first optical waveguide and the second optical waveguide is determined 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. The crosstalk measurement method according to feature 1. [Claim 4] 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 emitted light measured in the first measurement step and the power of the emitted light measured in the second measurement step. The crosstalk measurement method according to feature 3. [Claim 5] The wavelength width of the incident light is 1 nm or more. The crosstalk measurement method according to feature 1. [Claim 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 described above, the magnitude of crosstalk in the fan-in-fan-out device is removed, and the magnitude of the crosstalk between the first optical waveguide and the second optical waveguide is determined. The crosstalk measurement method according to any one of claims 1 to 5. [Claim 7] The optical device further includes a third optical waveguide arranged in parallel with the first optical waveguide. In the processing step described above, the magnitude of crosstalk between the first optical waveguide and the third optical waveguide is further determined based on the magnitude of crosstalk between the first optical waveguide and the second optical waveguide that was determined. The crosstalk measurement method according to any one of claims 1 to 5. [Claim 8] The optical device further includes a third optical waveguide arranged in parallel with the first optical waveguide. In the connection step, the other end of the first optical waveguide and the other end of the third optical waveguide are further optically connected via a second connecting optical waveguide having a different length from the first connecting optical waveguide. In the first measurement step, the output light is a pulsed light obtained by combining the light generated by the crosstalk of the incident light from the first optical waveguide to the third optical waveguide and the light generated by the crosstalk of the incident light entering the third optical waveguide from the first optical waveguide via the second connecting optical waveguide to the third optical waveguide from the third optical waveguide to the first optical waveguide, and the power of the output light emitted from one end of the first optical waveguide is further measured by the OTDR. In the processing step described above, the magnitude of the crosstalk between the first optical waveguide and the third optical waveguide is further determined using the power of the emitted light, which includes pulsed light generated by the crosstalk between the first optical waveguide and the third optical waveguide. The crosstalk measurement method according to any one of claims 1, 2, or 5. [Claim 9] The optical device further includes a third optical waveguide arranged in parallel with the second optical waveguide. In the connection step, one end of the second optical waveguide and one end of the third optical waveguide are further optically connected via the second connecting optical waveguide. In the first measurement step, the power of the emitted light emitted from one end of the first optical waveguide via the first connecting optical waveguide is further measured by the OTDR. The OTDR is used to measure the power of the emitted light emitted from one end of the first optical waveguide via the first connecting optical waveguide. The OTDR is used to measure the power of the emitted light emitted from one end of the first optical waveguide via the first connecting optical waveguide. In the processing step described above, the magnitude of the crosstalk between the second optical waveguide and the third optical waveguide is further determined using the power of the emitted light, which includes pulsed light generated by the crosstalk between the second optical waveguide and the third optical waveguide. The crosstalk measurement method according to any one of claims 1, 2, or 5. [Claim 10] The optical device further includes a third optical waveguide arranged in parallel with the first optical waveguide. In the aforementioned connection step, one end of the second optical waveguide and the other end of the third optical waveguide are further optically connected via the second connecting optical waveguide. In the first measurement step, the power of the emitted light emitted from one end of the first optical waveguide is further measured by the OTDR, including pulsed light resulting from the crosstalk between the incident light entering the first optical waveguide from the OTDR and the third optical waveguide, and the crosstalk between the incident light entering the third optical waveguide from the first optical waveguide via the first connecting optical waveguide, the second optical waveguide, and the second connecting optical waveguide, and the emitted light emitted from one end of the first optical waveguide. In the processing step described above, the magnitude of the crosstalk between the first optical waveguide and the third optical waveguide is further determined using the power of the emitted light, which includes pulsed light generated by the crosstalk between the first optical waveguide and the third optical waveguide. The crosstalk measurement method according to any one of claims 1, 2, or 5. [Claim 11] In the first measurement step, the OTDR further measures at least one of the light loss, reflectance, bending loss, and disconnection in the optical device. The crosstalk measurement method according to any one of claims 1, 2, or 5. [Claim 12] 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 the backscattered light per unit length generated in the first connecting optical waveguide is smaller than the power of the backscattered light per unit length generated in the first optical waveguide and the second optical waveguide, respectively. The crosstalk measurement method according to any one of claims 1, 2, or 5. [Claim 13] A crosstalk measuring device for an optical device having a first optical waveguide and a second optical waveguide arranged in parallel with each other, including one end and the other end, A first connecting optical waveguide optically connects the other end of the first optical waveguide to the other end of the second optical waveguide, An OTDR measures the power of the emitted light emitted from the one end of the first optical waveguide, which includes pulsed incident light incident from one end of the first optical waveguide, light generated by crosstalk between the incident light and the second optical waveguide, and light generated by crosstalk between the incident light incident from the first optical waveguide to the second optical waveguide via the first connecting optical waveguide and the second optical waveguide, and A processing unit that uses the measured power of the emitted light to determine the magnitude of crosstalk between the first optical waveguide and the second optical waveguide, Equipped with A crosstalk measuring device characterized by the following features.

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