Method for measuring inter-spatial-channel crosstalk, method for measuring inter-core crosstalk of multi-core optical fiber, device for measuring inter-spatial-channel crosstalk, and device for measuring inter-core crosstalk of multi-core optical fiber

Abstract

This inter-spatial-channel crosstalk measurement method is a method for measuring inter-spatial-channel crosstalk in a space-division multiplexing optical system that has a first input / output unit, a second input / output unit facing the first input / output unit, and a first spatial channel and a second spatial channel. The method includes: a first step of forming or providing a light reflecting surface on the second incident / incident portion; a second step of causing the test light to enter the first spatial channel at the first entrance / exit unit; a third step of reflecting at least a portion of the test light on the light reflecting surface; a fourth step of detecting a first optical power, which is the power of the light emitted from the first spatial channel at the first entrance / exit section, among at least a portion of the light, and a second optical power, which is the power of the light emitted from the second spatial channel at the first entrance / exit section, among at least a portion of the light; and a fifth step of calculating the magnitude of crosstalk between the first spatial channel and the second spatial channel on the basis of the first optical power and the second optical power.

Description

Technical Field

[0001] The present disclosure relates to a method for measuring spatial crosstalk between channels, a method for measuring inter-core crosstalk of a multi-core optical fiber, a device for measuring spatial crosstalk between channels, and a device for measuring inter-core crosstalk of a multi-core optical fiber.

[0002] This application claims the benefit of priority based on Japanese application No. 2023-021827, filed on February 15, 2023, and incorporates herein all the contents described in the Japanese application. Background Art

[0003] Patent Document 1 and Non-Patent Document 1 disclose methods for measuring inter-core crosstalk in multi-core optical fibers. In these methods, inter-core crosstalk is measured by injecting measurement light into a core at one end of the multi-core optical fiber and detecting the power of the measurement light emitted from that core and the other cores at the other end of the multi-core optical fiber.

[0004] Non-patent document 2 discloses a method for measuring inter-core crosstalk in multi-core optical fibers using an OTDR (Optical Time Domain Reflectometer) measurement method. In the method described in non-patent document 2, inter-core crosstalk is measured by injecting pulsed light into a core at one end of the multi-core optical fiber and detecting the temporal variation in the power of backscattered Rayleigh light (return light caused by Rayleigh scattering. Return light is light in which a portion of the incident light returns in the opposite direction of travel due to reflection, backscattering, etc.) emitted from that core and other cores at that end of the multi-core optical fiber.

[0005] Prior art literature

[0006] Patent Literature

[0007] Patent Document 1: International Publication No. 2012 / 115162

[0008] Non-patent literature

[0009] Non-patent document 1: Tetsuya Hayashi et al., "Characterization of Crosstalk in Ultra-Low-Crosstalk Multi-Core Fiber", Journal of Lightwave Technology, Vol.30, No.4, (2012)

[0010] Non-Patent Document 2: Masataka Nakazawa et al., “Nondestructive measurement of mode couplings along a multi-core fiber using a synchronous multi-channel OTDR”, Optics Express, Vol. 20, No. 11, (2012) Summary of the Invention

[0011] One aspect of the present disclosure relates to a method for measuring the inter-core crosstalk of a multi-core optical fiber, which has a first end and a second end opposite to the first end, and has a first fiber core and a second fiber core. The method comprises: a first step of forming or setting a light reflecting surface at the second end; a second step of causing test light to be incident on the first fiber core at the first end; a third step of causing at least a portion of the test light to be reflected on the light reflecting surface; a fourth step of detecting a first optical power and a second optical power, wherein the first optical power is the power of light emitted from the first fiber core in at least a portion of the light, and the second optical power is the power of light emitted from the second fiber core in at least a portion of the light; and a fifth step of calculating the magnitude of the crosstalk between the first fiber core and the second fiber core based on the first optical power and the second optical power. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 This is a diagram showing the configuration of a measuring device according to one embodiment of the present disclosure.

[0013] Figure 2 A diagram showing a cross section perpendicular to the central axis of a multi-core optical fiber.

[0014] Figure 3 It is a diagram showing the structure of a three-port optical coupler (optical circulator).

[0015] Figure 4 This is a diagram showing the structure of a modified example of the measuring device.

[0016] Figure 5 It is a diagram showing the structure of another modified example of the measuring device.

[0017] Figure 6 2 is a cross-sectional view showing an example of the light reflecting surface of the second end portion.

[0018] Figure 7 2 is a cross-sectional view showing an example of the light reflecting surface of the second end portion.

[0019] Figure 8 2 is a cross-sectional view showing an example of the light reflecting surface of the second end portion.

[0020] Figure 9 2 is a cross-sectional view showing an example of the light reflecting surface of the second end portion.

[0021] Figure 10 2 is a cross-sectional view showing an example of the light reflecting surface of the second end portion.

[0022] Figure 11 2 is a cross-sectional view showing an example of the light reflecting surface of the second end portion.

[0023] Figure 12 2 is a cross-sectional view showing an example of the light reflecting surface of the second end portion.

[0024] Figure 13 Graph schematically showing the temporal waveform of the optical power of continuous light.

[0025] Figure 14 Graph schematically showing the temporal waveform of the optical power of the chopped light.

[0026] Figure 15 Graph schematically showing the temporal waveform of the optical power of pulse light.

[0027] Figure 16 This is a flowchart illustrating a method for measuring inter-core crosstalk according to one embodiment.

[0028] Figure 17 This is a flowchart showing a modified example of the inter-core crosstalk measurement method.

[0029] Figure 18 This is a flowchart showing another modified example of the inter-core crosstalk measurement method.

[0030] Figure 19 This is a flowchart showing still another modified example of the inter-core crosstalk measurement method.

[0031] Figure 20 This is a graph showing the relationship between the measurement error of the inter-core crosstalk caused by Rayleigh backscattering and the transmission loss when the angle θ is changed by 1 degree from 0 to 6.

[0032] Figure 21 This is a graph showing the relationship between the maximum allowable transmission loss and the angle of the incident and exit surface of the multi-core optical fiber when the allowable measurement error is 2 dB, 1 dB, 0.5 dB, 0.2 dB, or 0.1 dB.

[0033] Figure 22 This is a graph schematically showing time waveforms of the power of light emitted from the first core into which the test light is incident and the power of light emitted from the second core when the test light is pulsed light.

[0034] Figure 23Figures illustrate the appearance of a holding portion included in a measurement device according to a first modification. Part (a) is a top view of the holding portion. Part (b) is a side view of the holding portion. Part (c) is a front view of the holding portion.

[0035] Figure 24 These are diagrams showing the appearance of a holding portion capable of holding a plurality of MCF core wires. Part (a) is a top view of the holding portion. Part (b) is a side view of the holding portion. Part (c) is a front view of the holding portion.

[0036] Figure 25 It is a diagram schematically showing a cross section of a dust cover of a storage and holding portion.

[0037] Figure 26 This is a diagram showing a state where the lid of the dust cover is opened.

[0038] Figure 27 This is a diagram schematically showing the configuration of a measuring device according to a reference example. DETAILED DESCRIPTION

[0039] [Technical Problems to be Solved by the Present Disclosure]

[0040] In conventional multi-core optical fiber crosstalk measurement, as described in Patent Document 1 and Non-Patent Document 1, test light is injected into a core at one end of the multi-core optical fiber, and the power of the test light emitted from that core and other cores is detected at the other end of the multi-core optical fiber. However, it is sometimes difficult to connect a light source that outputs the test light to one end of the multi-core optical fiber and a light detector to the other end of the multi-core optical fiber.

[0041] In contrast, the OTDR measurement method using backscattered Rayleigh light, as described in Non-Patent Document 2, allows test light to be injected and emitted from only one end of a multi-core optical fiber. However, because the power of backscattered Rayleigh light is very low, when crosstalk is low, the backscattered Rayleigh light detection signal is overwhelmed by noise, making it impossible to measure crosstalk.

[0042] The purpose of the present disclosure is to provide a spatial channel crosstalk measurement method, a multi-core optical fiber inter-core crosstalk measurement method, a spatial channel crosstalk measurement device, and a multi-core optical fiber inter-core crosstalk measurement device, which connects a light source and a light detector that output test light to one end of a multi-core optical fiber and can measure the size of the crosstalk even when the crosstalk is small.

[0043] [Effects of the Present Disclosure]

[0044] According to the present disclosure, a spatial channel crosstalk measuring method, a multi-core optical fiber core crosstalk measuring method, a spatial channel crosstalk measuring device, and a multi-core optical fiber core crosstalk measuring device can be provided, which connect a light source and a light detector that output test light to one end of a multi-core optical fiber and can measure the size of the crosstalk even when the crosstalk is small.

[0045] [Description of Embodiments of the Present Disclosure]

[0046] First, the contents of the embodiments of the present disclosure will be listed and described.

[0047] [1] One aspect of the present disclosure relates to a method for measuring spatial channel crosstalk of a space-division multiplexing optical system having a first input / output portion and a second input / output portion opposite to the first input / output portion, and having a first spatial channel and a second spatial channel. The measuring method includes a first step, a second step, a third step, a fourth step, and a fifth step. In the first step, a light reflecting surface is formed or set at the second input / output portion. In the second step, a test light is incident on the first spatial channel at the first input / output portion. In the third step, at least a portion of the test light is reflected on the light reflecting surface. In the fourth step, a first optical power and a second optical power are detected, wherein the first optical power is the power of at least a portion of the light emitted from the first spatial channel at the first input / output portion, and the second optical power is the power of at least a portion of the light emitted from the second spatial channel at the first input / output portion. In the fifth step, the magnitude of the crosstalk between the first spatial channel and the second spatial channel is calculated based on the first optical power and the second optical power.

[0048] In the measurement method of the above [1], it is sufficient to connect the light source and the light detector that output the test light to the first input and output part of the space-division multiplexing optical system, and there is no need to connect any of them to the second input and output part. Therefore, even when it is difficult to simultaneously connect the input and output parts of both sides of the space-division multiplexing optical system, the light source and the light detector can be easily connected. Furthermore, by halving the number of connections during measurement, the crosstalk measurement of the space-division multiplexing optical system can be efficiently performed. In addition, in the measurement method of the above [1], the magnitude of the crosstalk is calculated based on the power of the light reflected on the light reflection surface provided (or formed) at the second input and output part. The power of the light reflected on the light reflection surface is significantly greater than the power of the backward Rayleigh scattered light in the optical device during OTDR measurement. Therefore, even when the crosstalk is small, the detection signal will not be overwhelmed by the noise, and the crosstalk can be appropriately measured.

[0049] [2] In the measurement method of [1] above, the first optical power may be the sum of optical power components emitted from the first spatial channel, of the return optical power components of the test light including backscattered light at each position in the longitudinal direction of the spatial division multiplexing optical system. Furthermore, the second optical power may be the sum of optical power components emitted from the second spatial channel, of the return optical power components of the test light including backscattered light at each position in the longitudinal direction of the spatial division multiplexing optical system.

[0050] [3] In the measurement method of [2] above, the space-division multiplexing optical system may be a space-division multiplexing optical fiber, and the light reflecting surface may be an end face of the space-division multiplexing optical fiber. Alternatively, the wavelength of the test light may be set to λ (μm), the circumference of the circle may be set to π, the refractive index of the first spatial channel and the second spatial channel of the space-division multiplexing optical fiber may be set to n, and the transmission loss coefficient of the first spatial channel and the second spatial channel may be set to α (km -1 ), 0.5 times the mode field diameter of the first spatial channel and the second spatial channel is set to w (μm), the angle between the plane on the end face that touches the center of the first spatial channel and the second spatial channel and the plane that is orthogonal to the central axis of the space-division multiplexing optical fiber is set to φ (rad), the length of the space-division multiplexing optical fiber is set to L (km), the effective cross-sectional area of ​​the first spatial channel and the second spatial channel is set to A eff (μm 2 ), the Rayleigh scattering loss coefficients of the first spatial channel and the second spatial channel are set to α R (km -1 ), the value of mathematical formula (A) is 10 0.2 Furthermore, when the first optical power is PW1, the second optical power is PW2, and the magnitude of the crosstalk between the first spatial channel and the second spatial channel is XT, XT may be calculated using the mathematical formula (B).

[0051]

[0052] This allows the crosstalk measurement error due to backscattered Rayleigh light to be reduced to 10 dB or less. Alternatively, when evaluating crosstalk using equation (1) described below, the crosstalk measurement error due to backscattered Rayleigh light can be reduced to 2 dB or less. This allows for more accurate crosstalk measurement.

[0053] [4] In the measurement method of [2] above, the space-division multiplexing optical system may be a space-division multiplexing optical fiber, and the light reflecting surface may be an end face of the space-division multiplexing optical fiber. The angle formed by the plane on the end face that touches the center of the first spatial channel and the second spatial channel and the plane that is orthogonal to the central axis of the space-division multiplexing optical fiber is set as θ (degrees), and the loss coefficient of the first spatial channel and the second spatial channel is set as α dB (dB·km-1 ), when the length of the space division multiplexing optical fiber is set to L (km), the angle θ and the transmission loss α dB L satisfies mathematical formula (C).

[0054] α dB BL≤a0+a1θ+a2θ 2 …(C)

[0055] a0=-3.40×10 -1 [dB], a1=-3.73×10 -2 [dB / degree], a2=7.46×10 0 [dB / degree 2 ]

[0056] Furthermore, the wavelength of the test light may be less than or equal to 1.625 μm, and the effective cross-sectional area of ​​the first spatial channel and the second spatial channel at this wavelength may be 60 μm. 2 Furthermore, when the first optical power is PW1, the second optical power is PW2, and the magnitude of the crosstalk between the first spatial channel and the second spatial channel is XT, XT is calculated using equation (D).

[0057]

[0058] This makes it possible to reduce the crosstalk measurement error due to Rayleigh backscattered light to 10 dB or less, and thus to measure the crosstalk with higher accuracy.

[0059] [5] In the measurement method of [2] above, the space-division multiplexing optical system may be a space-division multiplexing optical fiber, and the light reflecting surface may be an end face of the space-division multiplexing optical fiber. Alternatively, the wavelength of the test light may be set to λ (μm), the circumference of the circle may be set to π, the refractive index of the first spatial channel and the second spatial channel of the space-division multiplexing optical fiber may be set to n, and the transmission loss coefficient of the first spatial channel and the second spatial channel may be set to α (km -1 ), 0.5 times the mode field diameter of the first spatial channel and the second spatial channel is set to w (μm), the angle between the plane on the end face that touches the center of the first spatial channel and the second spatial channel and the plane that is orthogonal to the central axis of the space-division multiplexing optical fiber is set to φ (rad), the length of the space-division multiplexing optical fiber is set to L (km), the effective cross-sectional area of ​​the first spatial channel and the second spatial channel is set to A eff (μm 2 ), the Rayleigh scattering loss coefficients of the first spatial channel and the second spatial channel are set to α R (km -1 ), when the first optical power is set to PW10, the second optical power is set to PW20, and the magnitude of the crosstalk between the first spatial channel and the second spatial channel is set to XT, mathematical formula (E) is used to calculate XT.

[0060]

[0061] [6] In the measurement method of [2] above, the space-division multiplexing optical system may be a space-division multiplexing optical fiber, the light reflecting surface may be an end face of the space-division multiplexing optical fiber, and the wavelength of the test light may be set to λ (μm), the circumference may be set to π, the refractive index of the first spatial channel and the second spatial channel of the space-division multiplexing optical fiber may be set to n, and the transmission loss coefficient of the first spatial channel and the second spatial channel may be set to α (km -1 ), the length of the space division multiplexing optical fiber is set to L (km), the effective cross-sectional area of ​​the first spatial channel and the second spatial channel is set to A eff (μm 2 ), the Rayleigh scattering loss coefficients of the first spatial channel and the second spatial channel are set to α R (km -1 ), when the first optical power is set to PW10 and the second optical power is set to PW20, mathematical formula (F) is used to calculate XT.

[0062]

[0063] [7] In the measurement method of [1] above, the fourth step may be such that the time-intensity waveform of the light emitted from the first spatial channel in the first input / output portion after being reflected in the first spatial channel, the second spatial channel, and the light reflecting surface, among the test light incident on the first spatial channel at the first input / output portion, is analyzed, and the power of the light reflected at a position in the longitudinal direction corresponding to the light reflecting surface and emitted from the first spatial channel is set as the first optical power. Furthermore, the fourth step may be such that the time-intensity waveform of the light emitted from the second spatial channel in the first input / output portion after being reflected in the first spatial channel, the second spatial channel, and the light reflecting surface, among the test light incident on the first spatial channel at the first input / output portion, is analyzed, and the power of the light reflected at a position in the longitudinal direction corresponding to the light reflecting surface and emitted from the second spatial channel is set as the second optical power.

[0064] [8] In the measurement methods of [1] to [7] above, the test light may be pulsed light. Furthermore, the first optical power and the second optical power may be the powers of light emitted from the first spatial channel and the second spatial channel, respectively, after the test light is incident on the first spatial channel in the second step and a delay time equal to twice the distance between the first incident and incident portion and the reflective surface has elapsed. This eliminates the influence of backscattered Rayleigh light from the first optical power and the second optical power, thereby enabling more accurate crosstalk measurement.

[0065] [9] In the measurement method of [7] or [8] above, the space-division multiplexing optical system may be a space-division multiplexing optical fiber, and the light reflecting surface may be an end face of the space-division multiplexing optical fiber. Alternatively, the wavelength of the test light may be λ (μm), the circumference of a circle may be π, the refractive index of the first spatial channel and the second spatial channel of the space-division multiplexing optical fiber may be n, 0.5 times the mode field diameter of the first spatial channel and the second spatial channel may be w (μm), the angle formed by the plane on the end face that touches the center of the first spatial channel and the second spatial channel and the plane that is orthogonal to the central axis of the space-division multiplexing optical fiber may be φ (rad), and the effective cross-sectional area of ​​the first spatial channel and the second spatial channel may be A. eff (μm 2 ), the Rayleigh scattering loss coefficients of the first spatial channel and the second spatial channel are set to α R (km -1 ), when the pulse width of the test light propagating in the first spatial channel and the second spatial channel in the space-division multiplexing optical fiber is set to T (km), the value of mathematical formula (G) is greater than 10.

[0066]

[0067] This allows the ratio (A1 / A2, the gain of the signal light due to reflection) of the power A1 of the pulsed light reflected on the light-reflecting surface (the first optical power and the second optical power) to the power A2 of the pulsed light generated immediately before reflection, excluding the backscattered Rayleigh light of the reflected light, to be 10 dB or greater. This allows for more accurate crosstalk measurement.

[0068]

[10] In the measurement methods of [1] to [9] above, the space-division multiplexing optical system may be a space-division multiplexing optical fiber or a space-division multiplexing optical device, the light reflecting surface may be an incident / output surface of the space-division multiplexing optical fiber or the space-division multiplexing optical device, and the first step may include forming the incident / output surface by cutting or cleaving the incident / output portion of the space-division multiplexing optical fiber or the space-division multiplexing optical device. This facilitates forming the light reflecting surface of the second incident / output portion.

[0069]

[11] In the measurement methods of [1] to

[10] above, the light reflecting surface may be an incident and exit surface of a space-division multiplexing optical system. Alternatively, the first step may include providing a reflective film on the incident and exit surface or immersing the incident and exit surface in liquid metal. This can increase the reflectivity of the light reflecting surface, further increasing the first optical power and the second optical power, thereby enabling more accurate crosstalk measurement.

[0070]

[12] In the measurement methods of [1] to

[11] above, the light reflecting surface may be an incident and exit surface of a space-division multiplexing optical system. Alternatively, the first step includes the step of configuring the incident and exit surface so as to be in contact only with the gas. This can increase the reflectivity of the light reflecting surface, further increasing the first optical power and the second optical power, thereby enabling more accurate crosstalk measurement.

[0071]

[13] In the measurement method of [1] above, the first step may include connecting the second incident and output surface of a second spatial division multiplexing optical system to the incident and output surface of the spatial division multiplexing optical system at the second incident and output portion, the second spatial division multiplexing optical system being different from the spatial division multiplexing optical system, and the first incident and output surface of the second spatial division multiplexing optical system being provided with a reflective film serving as a light reflecting surface. This can improve the reflectivity of the light reflecting surface, further increasing the first optical power and the second optical power, thereby enabling more accurate crosstalk measurement.

[0072]

[14] In the measurement method of [1] above, the first step may include the step of optically coupling the second incident and exit surfaces of the first single-core optical fiber and the second single-core optical fiber to the first spatial channel and the second spatial channel, respectively, at the second incident and exit portions, and the first incident and exit surfaces of the first single-core optical fiber and the second single-core optical fiber may be provided with a reflective film serving as a light reflecting surface. This can improve the reflectivity of the light reflecting surface, further increase the first optical power and the second optical power, and thereby measure crosstalk with higher accuracy.

[0073]

[15] In the measurement methods of [3] to [6], [9] and

[10] above, the space-division multiplexing optical fiber may be a multi-core optical fiber or a multimode optical fiber.

[0074]

[16] In the measurement method of [1] or [2] above, the space-division multiplexing optical system may be a multi-core optical device, a multi-core optical system, a multi-mode optical device or a multi-mode optical system.

[0075]

[17] In the measurement methods of [1] to

[16] above, the first spatial channel and the second spatial channel may be the first fiber core and the second fiber core, respectively, or the first mode and the second mode, respectively.

[0076]

[18] One aspect of the present disclosure relates to a method for measuring the inter-core crosstalk of a multi-core optical fiber, which is a method for measuring the inter-core crosstalk of a multi-core optical fiber having a first end and a second end opposite to the first end, and having a first fiber core and a second fiber core. The measuring method includes a first step, a second step, a third step, a fourth step, and a fifth step. In the first step, a light reflecting surface is formed or set at the second end. In the second step, a test light is incident on the first fiber core at the first end. In the third step, at least a portion of the test light is reflected on the light reflecting surface. In the fourth step, a first optical power and a second optical power are detected, wherein the first optical power is the power of at least a portion of the light emitted from the first fiber core at the first end, and the second optical power is the power of at least a portion of the light emitted from the second fiber core at the first end. In the fifth step, based on the first optical power and the second optical power, the magnitude of the crosstalk between the first fiber core and the second fiber core is calculated.

[0077] In the measurement method of the above-mentioned

[18] , it is sufficient to connect the light source and the light detector that output the test light to the first end of the multi-core optical fiber, and there is no need to connect any of them to the second end. Therefore, even in the case where it is not easy to simultaneously connect the two ends of the multi-core optical fiber, the light source and the light detector can be easily connected. Furthermore, by halving the number of connections during measurement, the crosstalk measurement of the multi-core optical fiber can be efficiently performed. In addition, in the measurement method of the above-mentioned

[18] , the magnitude of the crosstalk is calculated based on the power of the light reflected on the light reflection surface provided (or formed) at the second end. The power of the light reflected on the light reflection surface is significantly greater than the power of the backward Rayleigh scattered light in the optical fiber during OTDR measurement. Therefore, even in the case of small crosstalk, the detection signal will not be overwhelmed by the noise, and the crosstalk can be appropriately measured.

[0078]

[19] In the measurement method of

[18] above, the light reflecting surface may be the end face of the multi-core optical fiber. Alternatively, the first step includes forming a micro-scratch on the outer periphery of the optical fiber and then applying tensile stress and bending stress in the longitudinal axis direction of the optical fiber to cut (cleave) the second end of the multi-core optical fiber, thereby forming a roughly flat end face, and setting the roughly flat end face as the light reflecting surface. In this way, the light reflecting surface of the second end can be easily formed. As long as the cutting (cleave) is a method that can form a flat end face on the cut surface of the optical fiber, it can be a method different from the above, for example, laser cutting can also be used. If laser cutting is used, a more uniform end face can be formed, and the reflectivity can be made more uniform among multiple cores. Alternatively, when the second end is installed on a ferrule, capillary, V-groove, etc., the light reflecting surface can also be formed by grinding. A more uniform end face can be formed, and the reflectivity can be made more uniform among multiple cores.

[0079]

[20] In the measurement method of

[18] or

[19] above, the light reflecting surface may be an end face of a multi-core optical fiber. Alternatively, the first step may include providing a reflective film on the end face or immersing the end face in liquid metal. This can increase the reflectivity of the light reflecting surface, further increasing the first optical power and the second optical power, thereby enabling more accurate crosstalk measurement.

[0080]

[21] In the measurement method of

[18] or

[19] above, the light reflecting surface may be an end face of a multi-core optical fiber. Alternatively, the first step includes the step of configuring the end face so that it is in contact only with the gas. This can increase the reflectivity of the light reflecting surface, further increase the first optical power and the second optical power, and thereby measure crosstalk with higher accuracy.

[0081]

[22] In the measurement methods of

[18] to

[21] above, the test light may be pulsed light. Alternatively, the first optical power and the second optical power may be the powers of light emitted from the first and second optical cores, respectively, after the test light is incident on the first core in the second step and a delay time equal to twice the optical distance between the first end and the reflecting surface has elapsed. This allows the influence of backscattered Rayleigh light to be eliminated from the first and second optical powers, thereby enabling more accurate crosstalk measurement.

[0082]

[23] In the measurement method of

[22] above, the light reflecting surface may be the end face of the multi-core optical fiber. Alternatively, the wavelength of the test light may be λ (μm), the circumference may be π, the refractive index of the core of the multi-core optical fiber may be n, 0.5 times the mode field diameter of the first core and the second core may be w (μm), the angle between the plane connecting the center of the first core and the second core and the end face and the plane perpendicular to the central axis of the multi-core optical fiber may be φ (rad), and the effective cross-sectional area of ​​the first core and the second core may be A. eff (μm 2 ), the Rayleigh scattering loss coefficient of the first core and the second core is set to α R (km -1 ), when the pulse width of the test light propagating in the core of the multi-core optical fiber is set to T (km), the value of the mathematical formula (H) is greater than 10.

[0083]

[0084] This allows the ratio (A1 / A2, the gain of the signal light due to reflection) of the power A1 of the pulsed light reflected on the light-reflecting surface (the first optical power and the second optical power) to the power A2 of the pulsed light generated immediately before reflection, excluding the backscattered Rayleigh light of the reflected light, to be 10 dB or greater. This allows for more accurate crosstalk measurement.

[0085]

[24] In the measurement method of

[18] , the first step may include the step of connecting the second end face of the second multi-core optical fiber to the end face of the multi-core optical fiber at the second end portion, the second multi-core optical fiber being different from the multi-core optical fiber, and the first end face of the second multi-core optical fiber being provided with a reflective film as a light reflecting surface. This can increase the reflectivity of the light reflecting surface, further increase the first optical power and the second optical power, and thereby measure crosstalk with higher accuracy.

[0086]

[25] In the measurement method of

[18] , the first step may include the step of optically coupling the second end faces of the first single-core optical fiber and the second single-core optical fiber to the first core and the second core, respectively, at the second end portion, and the first end faces of the first single-core optical fiber and the second single-core optical fiber are provided with a reflective film as a light reflecting surface. This can improve the reflectivity of the light reflecting surface, further increase the first optical power and the second optical power, and thus measure crosstalk with higher accuracy.

[0087]

[26] An apparatus for measuring spatial channel crosstalk according to one aspect of the present disclosure is an apparatus for measuring spatial channel crosstalk of a space-division multiplexing optical system having a first input / output section and a second input / output section opposite to the first input / output section, and having N (N is an integer greater than or equal to 2) spatial channels. The measuring apparatus comprises a light source section, a light detection section, and a calculation section. The light source section causes test light to be incident on the N spatial channels at the first input / output section. The light detection section detects a first optical power and a second optical power. The first optical power is the power of light emitted from the first spatial channel into which the test light is incident, in at least a portion of the test light reflected on the light reflection surface formed or provided on the second input / output section. The second optical power is the power of light emitted from a second spatial channel different from the first spatial channel, in at least a portion of the light. The calculation section calculates the magnitude of the crosstalk between the first spatial channel and the second spatial channel based on the first optical power and the second optical power.

[0088] In the measuring device of the above-mentioned

[26] , it is sufficient to connect the light source unit and the light detection unit to the first input and output unit of the space-division multiplexing optical system, and there is no need to connect any of them to the second input and output unit. Therefore, even in the case where it is difficult to simultaneously access the input and output units of both sides of the space-division multiplexing optical system, the light source and the light detector can be easily connected. Furthermore, by halving the number of connections during measurement, the crosstalk measurement of the space-division multiplexing optical system can be efficiently performed. In addition, in the measuring device of the above-mentioned

[26] , the magnitude of the crosstalk is calculated based on the power of the light reflected on the light reflecting surface provided (or formed) at the second end. The power of the light reflected on the light reflecting surface is significantly greater than the power of the backward Rayleigh scattered light during OTDR measurement. Therefore, even in the case of small crosstalk, the detection signal will not be drowned out by the noise, and the crosstalk can be appropriately measured.

[0089]

[27] Alternatively, the spatial channel crosstalk measurement device of

[26] further includes N three-port optical couplers and optical components. The N three-port optical couplers have a first port, a second port, and a third port, and output the light input to the first port from the second port and output the light input to the second port from the third port. The optical component optically couples the N spatial channels in the first input and output portion of the space-division multiplexing optical system to the second ports of the N three-port optical couplers, respectively. The light source portion is optically coupled to the first port of the N three-port optical couplers. The optical detection portion is optically coupled to the third port of the N three-port optical couplers. Thus, the following structure can be simply realized: the test light from the light source portion is incident on the N fiber cores, respectively, and the light emitted from the first fiber core and the light emitted from the second fiber core are detected in the optical detection portion.

[0090]

[28] Alternatively, in the spatial channel crosstalk measurement device of

[27] , the light source unit may include N light sources, and the N light sources may be optically coupled to the first ports of the N three-port optical couplers, respectively. Thus, a test light can be input to the first ports of the N three-port optical couplers using a simple structure.

[0091]

[29] In the spatial channel crosstalk measurement device of

[27] , the light source unit may include a single light source and a first optical switch. The first optical switch selectively optically couples the single light source to the first port of any one of the N three-port optical couplers. This reduces the number of light sources.

[0092]

[30] In the spatial channel crosstalk measurement devices of

[27] to

[29] above, the light detection unit may include N optical receivers. Alternatively, the N optical receivers may be optically coupled to the third ports of the N three-port optical couplers. This allows detection of light output from the third ports of the N three-port optical couplers using a simple structure.

[0093]

[31] In the spatial channel crosstalk measurement devices of

[27] to

[29] above, the optical detection unit may include a single optical receiver and a second optical switch. The second optical switch selectively optically couples the single optical receiver to the third port of any one of the N three-port optical couplers. This reduces the number of optical receivers.

[0094]

[32] In the spatial channel crosstalk measurement device of

[26] to

[31] above, the time-intensity waveform of the light emitted from the first spatial channel in the first input / output portion after being reflected in the first spatial channel, the second spatial channel, and the light reflecting surface, among the test light incident on the first spatial channel at the first input / output portion, may be analyzed, and the first optical power is the power of the light reflected from the first spatial channel at a position corresponding to the length direction of the light reflecting surface. Furthermore, the time-intensity waveform of the light emitted from the second spatial channel in the first input / output portion after being reflected in the first spatial channel, the second spatial channel, and the light reflecting surface, among the test light incident on the first spatial channel at the first input / output portion, may be analyzed, and the second optical power is the power of the light reflected from the second spatial channel at a position corresponding to the length direction of the light reflecting surface.

[0095]

[33] In the spatial channel crosstalk measurement devices of

[26] to

[31] above, the test light may be pulsed light. Alternatively, the first optical power and the second optical power may be the power of light emitted from the first spatial channel and the second spatial channel, respectively, after the test light is incident on the first spatial channel and a delay time equal to twice the distance between the first incident and incident portion and the reflective surface has elapsed. This eliminates the influence of Rayleigh backscattered light from the first optical power and the second optical power, thereby enabling more accurate crosstalk measurement.

[0096]

[34] In the spatial channel crosstalk measurement device of

[26] to

[33] above, the light reflecting surface may be an incident and exit surface of the spatial division multiplexing optical system. The spatial channel crosstalk measurement device may further include a holding unit for holding the spatial division multiplexing optical system so that the incident and exit surface is in contact only with the gas.

[0097]

[35] Alternatively, the spatial channel crosstalk measurement device of

[26] to

[33] further includes a second spatial division multiplexing optical system, wherein the first incident surface of the second spatial division multiplexing optical system is provided with a reflective film serving as a light reflecting surface. Alternatively, the second incident surface of the second spatial division multiplexing optical system is connected to the incident surface of the spatial division multiplexing optical system at the second incident and output portion. This improves the reflectivity of the light reflecting surface, further increasing the first optical power and the second optical power, thereby enabling more accurate crosstalk measurement.

[0098]

[36] Alternatively, the spatial channel crosstalk measurement device of

[26] to

[33] further includes N single spatial channel optical fibers, wherein the first incident and output surfaces of the single spatial channel optical fibers are provided with a reflective film serving as a light reflecting surface. Alternatively, the second incident and output surfaces of the N single spatial channel optical fibers are optically coupled to the N spatial channels at the second incident and output portions. This improves the reflectivity of the light reflecting surfaces, further increasing the first optical power and the second optical power, thereby enabling more accurate crosstalk measurement.

[0099]

[37] In the spatial channel crosstalk measuring device described in

[26] to

[36] above, the space-division multiplexing optical system may be a space-division multiplexing optical fiber.

[0100]

[38] In the spatial channel crosstalk measuring device of the above-mentioned

[37] , the spatial division multiplexing optical fiber may be a multi-core optical fiber or a multi-mode optical fiber.

[0101]

[39] In the spatial channel crosstalk measuring device described in

[26] to

[36] above, the spatial division multiplexing optical system may be a multi-core optical device, a multi-core optical fiber, a multi-mode optical device, a multi-mode optical fiber, or an optical system formed by optically coupling two or more of these.

[0102]

[40] In the spatial channel crosstalk measurement device described in

[26] to

[36] above, the first spatial channel and the second spatial channel may be the first fiber core and the second fiber core, respectively, or the first mode and the second mode, respectively.

[0103]

[41] An inter-core crosstalk measuring device for a multi-core optical fiber according to one aspect of the present disclosure is a device for measuring the inter-core crosstalk of a multi-core optical fiber having a first end and a second end opposite to the first end and having N (N is an integer greater than or equal to 2) cores. The device comprises a light source unit, a light detection unit, and a calculation unit. The light source unit causes test light to be incident on the N cores at the first end. The light detection unit detects a first optical power and a second optical power, wherein the first optical power is the power of light emitted from the first core into which the test light is incident, in at least a portion of the test light reflected on the light reflection surface formed or provided at the second end, and the second optical power is the power of light emitted from a second core different from the first core, in at least a portion of the light. The calculation unit calculates the magnitude of the crosstalk between the first core and the second core based on the first optical power and the second optical power.

[0104] In the measuring device of the above-mentioned

[41] , it is sufficient to connect the light source unit and the light detection unit to the first end of the multi-core optical fiber, and there is no need to connect any of them to the second end. Therefore, even in the case where it is not easy to connect both ends of the multi-core optical fiber at the same time, the light source and the light detector can be easily connected. Furthermore, by halving the number of connections during measurement, the crosstalk measurement of the multi-core optical fiber can be efficiently performed. In addition, in the measuring device of the above-mentioned

[41] , the magnitude of the crosstalk is calculated based on the power of the light reflected on the light reflection surface provided (or formed) at the second end. The power of the light reflected on the light reflection surface is significantly greater than the power of the backward Rayleigh scattered light during OTDR measurement. Therefore, even in the case of small crosstalk, the detection signal will not be overwhelmed by the noise, and the crosstalk can be appropriately measured.

[0105]

[42] Alternatively, the measuring device of

[41] further includes N optical circulators and optical components. The N optical circulators have a first port, a second port, and a third port, and output light input to the first port from the second port and output light input to the second port from the third port. The optical component optically couples the N cores in the first end portion of the multi-core optical fiber to the second ports of the N optical circulators, respectively. The light source unit is optically coupled to the first ports of the N optical circulators. The optical detection unit is optically coupled to the third ports of the N optical circulators. Thus, the following structure can be easily realized: the test light from the light source unit is incident on the N cores, respectively, and the light emitted from the first core and the light emitted from the second core are detected in the optical detection unit.

[0106]

[43] In the measurement device of

[42] , the light source unit may include N light sources, and the N light sources may be optically coupled to the first ports of the N optical circulators, respectively. This allows the test light to be input to the first ports of the N optical circulators with a simple structure.

[0107]

[44] In the measuring device of

[42] above, the light source unit may include a single light source and a first optical switch. The first optical switch selectively optically couples the single light source to the first port of any one of the N optical circulators. This can reduce the number of light sources.

[0108]

[45] In the measurement device of any one of

[42] to

[44] above, the light detection unit may include N optical receivers. Alternatively, the N optical receivers may be optically coupled to the third ports of the N optical circulators. This allows detection of light output from the third ports of the N optical circulators using a simple structure.

[0109]

[46] In the measuring device of

[43] or

[44] above, the optical detection unit may include a single optical receiver and a second optical switch. The second optical switch selectively optically couples the single optical receiver to the third port of any one of the N optical circulators. This reduces the number of optical receivers.

[0110]

[47] In the measurement device of any one of

[41] to

[46] above, the test light may be pulsed light. Alternatively, the first optical power and the second optical power may be the power of light emitted from the first core and the second core, respectively, after the test light is incident on the core and a delay time equivalent to twice the optical distance between the first end and the reflecting surface has elapsed. Thus, the influence of backscattered Rayleigh light can be eliminated from the first optical power and the second optical power, thereby enabling more accurate crosstalk measurement.

[0111]

[48] ​​In the measurement device of any one of

[41] to

[47] above, the light reflecting surface may be an end face of a multi-core optical fiber. Alternatively, the measurement device may further include a holding portion for holding the multi-core optical fiber so that the end face is in contact only with the gas. This can increase the reflectivity of the light reflecting surface, further increasing the first optical power and the second optical power, thereby enabling more accurate crosstalk measurement.

[0112]

[49] Alternatively, the measuring device of any one of

[41] to

[47] further comprises a second multi-core optical fiber, wherein the first end face of the second multi-core optical fiber is provided with a reflective film serving as a light reflecting surface. The second end face of the second multi-core optical fiber is connected to the end face of the multi-core optical fiber at the second end portion. This can increase the reflectivity of the light reflecting surface, further increasing the first optical power and the second optical power, thereby enabling more accurate crosstalk measurement.

[0113]

[50] Alternatively, the measuring device of any one of

[41] to

[47] further comprises N single-core optical fibers, wherein the first end faces of the single-core optical fibers are provided with a reflective film serving as a light-reflecting surface. The second end faces of the N single-core optical fibers are optically coupled to the N cores at their respective second ends. This increases the reflectivity of the light-reflecting surface, further increasing the first optical power and the second optical power, thereby enabling more accurate crosstalk measurement.

[0114] [Details of the embodiments of the present disclosure]

[0115] Specific examples of the spatial channel crosstalk measurement method, the multi-core optical fiber core crosstalk measurement method, the spatial channel crosstalk measurement device, and the multi-core optical fiber core crosstalk measurement device according to the present embodiment are described with reference to the accompanying drawings as needed. The present invention is not limited to these examples, but is shown by the claims and is intended to include all changes within the meaning and scope equivalent to the claims. In the following description, the same elements are marked with the same reference numerals in the description of the drawings, and repeated descriptions are omitted.

[0116] Figure 1This figure shows the structure of a measuring device 1A according to one embodiment of the present disclosure. The measuring device 1A is a device for measuring crosstalk between spatial channels in a space division multiplexing (SDM) optical system. The concept of an SDM optical system includes SDM optical fibers, SDM optical devices, and systems consisting of one or more SDM optical fibers optically coupled to one or more SDM optical devices. For example, an SDM optical fiber is a multi-core fiber (MCF) having multiple cores within a single fiber, or a multimode fiber having multiple spatial modes (also called propagation modes or waveguide modes) within a single core. Each core of an MCF has one or more spatial modes. Therefore, there are also optical fibers that are both MCFs and MMFs. SDM optical fibers include all optical fibers that have multiple spatial modes within a single fiber. The spatial channels within an SDM optical fiber are equivalent to spatial modes. The concept of an SDM optical device includes optical devices other than SDM optical fibers that have multiple spatial channels, such as optical waveguide chips and fan-outs for SDM fibers (such as fan-outs for spatial optical systems, fiber bundle fan-outs, and optical waveguide fan-outs). For example, in an optical device having a core such as an optical waveguide chip, an optical fiber bundle fan-out, or an optical waveguide fan-out, a spatial mode corresponds to a spatial channel. In an SDM optical device of a spatial optical system, in the portion where light propagates in free space, a spatial channel does not necessarily correspond to a spatial mode. However, the SDM optical device of the spatial optical system is optically coupled with other optical fibers or optical devices at the input and output portions. Therefore, the optical path in the SDM optical device of the spatial optical system that corresponds to the spatial mode of other optical fibers or optical devices corresponds to a spatial channel. The concept of an SDM optical system includes, for example, SDM optical fibers and SDM optical devices that are optically coupled or connected to each other. An SDM optical system has multiple spatial channels. In the following description, an apparatus for measuring the inter-core crosstalk of MCF10, which is an example of an SDM optical system, is described.

[0117] First, the structure of the MCF 10 will be described. The MCF 10 includes a first end portion (first incident and output portion) 10a and a second end portion (second incident and output portion) 10b opposite to the first end portion 10a. Figure 2 : is a diagram showing a cross section perpendicular to the central axis of MCF10. Figure 2As shown, MCF10 has a glass fiber 11 and a coating resin 12 that covers the outer peripheral surface of the glass fiber 11. The glass fiber 11 has N cores as N (N is an integer greater than or equal to 2) spatial channels. In the example shown in the figure, the glass fiber 11 has four (i.e., N=4) cores 13a, 13b, 13c, and 13d. Furthermore, the glass fiber 11 has a cladding 14. Furthermore, the glass fiber 11 may also have a mark 15. In the example shown in the figure, in a cross section perpendicular to the central axis of the MCF10, the cores 13a, 13b, 13c, and 13d are arranged at equal intervals on concentric circles centered on the central axis of the MCF10. The cladding 14 is a common cladding that surrounds the cores 13a, 13b, 13c, and 13d and the mark 15. The mark 15 has a refractive index different from that of the cladding 14.

[0118] Refer again Figure 1 The measuring device 1A includes a light source unit 20A, a light detection unit 30A, a circulator unit (photocoupler unit) 40 , a fan-in / fan-out (FIFO) 50 , and a calculation unit 60 .

[0119] The light source unit 20A emits test light that enters any one of the fiber cores 13a, 13b, 13c, and 13d at the first end portion 10a. The light source unit 20A of this embodiment includes a single light source 21 and a first optical switch 22. The first optical switch 22 has at least one input port 22a and the same number of output ports 22b, 22c, 22d, and 22e as the number of fiber cores 13a, 13b, 13c, and 13d. The first optical switch 22 selectively optically couples the input port 22a to any one of the output ports 22b, 22c, 22d, and 22e. The input port 22a is optically coupled to the light source 21.

[0120] The light detection unit 30A detects light emitted from each of the fiber cores 13a, 13b, 13c, and 13d at the first end 10a. The light detection unit 30A of this embodiment includes a single optical receiver (power meter) 31 and a second optical switch 32. The second optical switch 32 has at least one output port 32a and the same number of input ports 32b, 32c, 32d, and 32e as the fiber cores 13a, 13b, 13c, and 13d. The second optical switch 32 selectively optically couples the output port 32a to any one of the input ports 32b, 32c, 32d, and 32e. The output port 32a is optically coupled to the light receiver 31.

[0121] The circulator unit 40 includes optical circulators 41 , 42 , 43 , and 44 , which are three-port optical couplers, and have the same number as the cores 13 a , 13 b , 13 c , and 13 d . Figure 3 4 is a diagram showing the structure of the optical circulator 41. The structures of the optical circulators 42, 43, and 44 are the same as that of the optical circulator 41. Figure 3 As shown, the optical circulator 41 has a first port P1, a second port P2, and a third port P3. The optical circulator 41 outputs light L1 input to the first port P1 from the second port P2 with low loss, and outputs light L2 input to the second port P2 from the third port P3 with low loss. Light L1 input to the first port P1 is rarely output from the third port P3. Light L2 input to the second port P2 is rarely output from the first port P1. Light input to the third port P3 is rarely output from both the first port P1 and the second port P2.

[0122] The insertion loss from the first port P1 to the second port P2 is, for example, 1 dB or less. The insertion loss from the first port P1 to the third port P3 is, for example, 30 dB or more or 40 dB or more. The insertion loss from the second port P2 to the third port P3 is, for example, 1 dB or less. The insertion loss from the second port P2 to the first port P1 is, for example, 30 dB or more or 40 dB or more. The insertion loss from the third port P3 to the first port P1 and the second port P2 is, for example, 30 dB or more or 40 dB or more.

[0123] Refer again Figure 1 The first ports P1 of the optical circulators 41, 42, 43, and 44 are optically coupled to the output ports 22b, 22c, 22d, and 22e of the first optical switch 22, respectively. Thus, the first optical switch 22 can selectively optically couple the light source 21 to the first port P1 of any one of the optical circulators 41, 42, 43, and 44. The third ports P3 of the optical circulators 41, 42, 43, and 44 are optically coupled to the input ports 32b, 32c, 32d, and 32e of the second optical switch 32, respectively. Thus, the second optical switch 32 can selectively optically couple the optical receiver 31 to the third port P3 of any one of the optical circulators 41, 42, 43, and 44. In the above description, three-port optical circulators 41, 42, 43, and 44 are used as examples of three-port optical couplers. However, the three-port optical coupler is not limited to this. Alternatively, a 1×2 fiber coupler or a 2×2 fiber coupler with one port terminated to suppress reflection can be used. Using a fused fiber coupler as the fiber coupler can suppress reflection within the fiber coupler. Alternatively, the fiber coupler may be a waveguide fiber coupler.

[0124] If the three-port optical coupler is a 1×2 fiber coupler or a 2×2 fiber coupler with one port terminated to suppress reflection, the three-port optical coupler has a first port P1, a second port P2, and a third port P3. The three-port optical coupler outputs light L1 input to the first port P1 from the second port P2 with low loss, and outputs light L2 input to the second port P2 from the third port P3 with low loss. Light L1 input to the first port P1 is barely output from the third port P3. Light L2 input to the second port P2 is barely output from the first port P1, and light input to the third port P3 is also barely output from both sides of the second port P2, but this has no significant effect on the measurement. Light input to the third port P3 is barely output from the first port P1. However, in a 1×2 fiber coupler or a 2×2 fiber coupler with one port terminated with reflection suppression, the insertion loss between ports P1 and P2, and the insertion loss between ports P2 and P3, which have low insertion loss, is higher than that in an optical circulator. This is because, for example, when a 1×2 fiber coupler or a 2×2 fiber coupler is an optical power divider with a 50:50 splitting ratio, a loss of approximately 3 dB occurs as a principle loss.

[0125] The insertion loss from the first port P1 to the second port P2 is, for example, 4 dB or less. The insertion loss from the first port P1 to the third port P3 is, for example, 40 dB or more or 50 dB or more. The insertion loss from the second port P2 to the third port P3 is, for example, 4 dB or less. The insertion loss from the third port P3 to the first port P1 is, for example, 40 dB or more or 50 dB or more.

[0126] FIFO 50 is an optical component that optically couples the fiber cores 13a, 13b, 13c, and 13d in the first end 10a of MCF 10 to the second ports P2 of optical circulators 41, 42, 43, and 44, respectively. FIFO 50 includes an input / output port 50a connected to MCF 10, and input / output ports 50b, 50c, 50d, and 50e connected to the second ports P2 of optical circulators 41, 42, 43, and 44, respectively. The input / output port 50a of FIFO 50 is formed, for example, by etching and tapering the tip ends of a number of single-core fibers equal to the number of cores 13a, 13b, 13c, and 13d of MCF 10, and then bundling these tip ends. In this bundle at the tip, the spacing between the cores of the single-core fibers is the same as the spacing between the cores 13a, 13b, 13c, and 13d of MCF 10. The bundle at the front end contacts the first end 10a of the MCF 10, optically coupling the first end of each single-core fiber to the cores 13a, 13b, 13c, and 13d, respectively. The second end of each single-core fiber forms an input / output port 50b, 50c, 50d, and 50e, respectively, and is optically coupled to the second port P2 of each optical circulator 41, 42, 43, and 44.

[0127] The calculation unit 60 calculates the magnitude of inter-core crosstalk based on the detection results of the light detection unit 30A. The calculation unit 60 is composed of, for example, a computer including a CPU, memory, and storage. The storage device stores software for calculating the magnitude of inter-core crosstalk. The CPU reads and executes the software to calculate the magnitude of inter-core crosstalk. The calculation unit 60 is electrically (or communicatively) connected to the light receiver 31.

[0128] Figure 4 This is a diagram showing the structure of a measuring device 1B as a modified example of the measuring device 1A. The measuring device 1B includes a light detecting unit 30B instead of Figure 1 The optical detection unit 30A is shown. The optical detection unit 30B includes the same number of optical receivers (power meters) 33, 34, 35, and 36 as the cores 13a, 13b, 13c, and 13d of the MCF 10. The optical receivers 33, 34, 35, and 36 are optically coupled to the third ports P3 of the optical circulators 41, 42, 43, and 44, respectively. The computing unit 60 is electrically (or communicatively) connected to the optical receivers 33, 34, 35, and 36.

[0129] Figure 5 1A is a diagram showing a configuration of a measuring device 1C as another modified example of the measuring device 1A. The measuring device 1C includes a light source unit 20B instead of Figure 1The light source unit 20A is shown. The light source unit 20B includes the same number of light sources 23, 24, 25, and 26 as the cores 13a, 13b, 13c, and 13d of the MCF 10. The light sources 23, 24, 25, and 26 are optically coupled to the first ports P1 of the optical circulators 41, 42, 43, and 44, respectively. The measurement device may include a light detection unit 30B instead of the light detection unit 30A, and a light source unit 20B instead of the light source unit 20A.

[0130] Here, an example embodiment of the second end portion 10b of the MCF 10 is described. A light-reflecting surface is formed or provided at the second end portion 10b. This light-reflecting surface reflects at least a portion of the test light propagating from the first end portion 10a to the second end portion 10b through each of the cores 13a, 13b, 13c, and 13d. The light-reflecting surface is configured to reflect the test light at a reflectivity of 0.001 or greater, 0.01 or greater, 0.1 or greater, or 0.5 or greater. Figures 6 to 12 It is a cross-sectional view showing an example of the light reflecting surface of the second end portion 10b, showing a cross section along the central axis AX of the glass fiber 11 of the MCF10. In these figures, the illustration of the coating resin 12 is omitted. The second end portion 10b includes the end face (incident and exit faces) 11a of the glass fiber 11. Here, if the power of the light incident on the light reflecting surface is set to Pi and the power of the light reflected by the light reflecting surface is set to Pr, the reflectivity can be defined by Pr / Pi. In IEC-61300-3-6, the value obtained by multiplying the decibel value of the reflectivity (Pr / Pi) by -1 is defined as Return Loss. In addition, the method for measuring Retern Loss is illustrated, so the reflectivity of the light reflecting surface can also be measured by the method described in IEC-61300-3-6.

[0131] exist Figure 6 In the example shown, the end face 11a of the glass fiber 11 is a light-reflecting surface that reflects at least a portion of the test light due to the refractive index difference between the glass fiber 11 and the external medium (e.g., air). In this example, the end face 11a is a flat surface that has been cut or polished. In this example, the end faces 131 of the cores 13a, 13b, 13c, and 13d are aligned with the end face 11a without any height difference (the end faces 131 may be recessed or protruded relative to the end face 11a by less than 1 μm). When defining an imaginary plane H2 parallel to the end face 11a, the centers of the end faces 131 of the cores 13a, 13b, 13c, and 13d on the end face 11a touch the imaginary plane H2. The imaginary plane H2 forms an angle φ with an imaginary plane H1 perpendicular to the central axis AX of the MCF 10. Angle φ is defined using the radian method (unit: rad). In one example, angle φ is greater than 0 rad and less than 2π / 180 rad.

[0132] exist Figure 7In the example shown, the end face 11a of the glass fiber 11 is also a light reflecting surface that reflects at least a portion of the test light due to the refractive index difference between the glass fiber 11 and the external medium (such as air). However, the end face 11a of this example is not flat, but a curved surface that convexes toward the outside, that is, the external medium. In this example, the end faces 131 of the cores 13a, 13b, 13c, and 13d are surfaces aligned with the end face 11a without any height difference (the end face 131 may also be concave or convex with respect to the end face 11a by a sufficient amount less than 1 μm). On the end face 11a, an imaginary plane H2a is defined that is connected to the center of the end faces 131 of the cores 13a, 13b, 13c, and 13d. At this time, the imaginary plane H2a forms an angle φ with the imaginary plane H1 that is orthogonal to the center axis AX of the MCF10. The range of the angle φ is the same as Figure 6 Same way as shown.

[0133] exist Figure 8 In the example shown, a reflective film 71 is provided on the end face 11a of the glass fiber 11. The reflective film 71 is, for example, a dielectric multilayer film or a metal film. The interface between the reflective film 71 and the glass fiber 11 (i.e., the end face 11a) is a light reflecting surface that reflects at least a portion of the test light.

[0134] exist Figure 9 In the example shown, a reflective member 72 is provided on the end face 11a of the glass fiber 11. The reflective member 72 extends from the end face 11a to the side of the glass fiber 11 and surrounds the second end portion 10b. The reflective member 72 may be, for example, a dielectric multilayer film, a metal film, or liquid metal. The interface between the reflective member 72 and the glass fiber 11 (i.e., the end face 11a) serves as a light-reflecting surface that reflects at least a portion of the test light.

[0135] exist Figure 10 In the example shown, the end face 11a of the glass fiber 11 is immersed in liquid metal 74. The liquid metal 74 is contained in a container 73 with an upper opening, and the end face 11a of the glass fiber 11 is immersed in the liquid metal 74 from above. Since the end face 11a is in contact with the liquid metal 74, the interface between the liquid metal 74 and the glass fiber 11 (i.e., the end face 11a) becomes a light reflecting surface that reflects at least a portion of the test light.

[0136] exist Figure 11In the example shown, the measuring device 1A, 1B, or 1C further includes a reflection enhancement device 80 at the second end 10b of the MCF 10. The reflection enhancement device 80 includes an MCF 81 that is different from the MCF 10, and a reflective film 82 provided on the first end face 81a of the MCF 81. The reflective film 82 is, for example, a dielectric multilayer film or a metal film. The second end face of the MCF 81 is connected to the end face 11a of the MCF 10 at the second end 10b. That is, the MCF 81 has the same number of cores as the cores 13a, 13b, 13c, and 13d of the MCF 10 (only two cores 83a and 83b are shown in the figure), and these cores are optically coupled to the cores 13a, 13b, 13c, and 13d of the MCF 10, respectively. The connection between the MCF 81 and the MCF 10 can be a fusion connection or a connection based on an optical connector. In this example, the reflective film 82 constitutes a light reflecting surface that reflects at least a portion of the test light.

[0137] exist Figure 12 In the example shown, the measurement apparatus 1A, 1B, or 1C further includes a reflection enhancement device 90 at the second end 10b of the MCF 10. This reflection enhancement device 90 includes a number of single-core fibers (SCFs) 92 and a FIFO 91, the same number as the cores 13a, 13b, 13c, and 13d of the MCF 10. A reflective film 93, which serves as a light-reflecting surface for reflecting at least a portion of the test light, is provided on the first end face 92a of each SCF 92. The reflective film 93 is, for example, a dielectric multilayer film or a metal film. The second end face of each SCF 92 is optically coupled to the cores 13a, 13b, 13c, and 13d in the second end 10b via the FIFO 91.

[0138] Refer again Figure 1 The test light output from the light source unit 20A may be any of continuous light, chopped light, and pulsed light. Figure 13 This graph schematically illustrates the time waveform of the optical power of continuous light. When the test light is continuous light, its optical power remains constant regardless of time. Furthermore, when the test light is continuous light, a typical optical power meter can be used as the optical receivers 31, 33, 34, and 35. Figure 14 This graph schematically illustrates the temporal waveform of the optical power of chopped light. When the test light is chopped light, the temporal waveform of the optical power is a rectangular wave. The duty cycle (the ratio of the time when the optical power is at its peak to the total time) is, for example, 0.5 or 0.25. When the test light is chopped light, using an optical power meter compatible with chopped detection (synchronous detection, phase detection) as optical receivers 31, 33, 34, and 35 allows for detection that suppresses measurement noise caused by ambient light, etc., thereby improving detection sensitivity. Figure 15This graph schematically illustrates the temporal waveform of the optical power of pulsed light. When the test light is pulsed, multiple pulse waveforms repeat at a predetermined period. Repeated measurements and averaging can suppress measurement noise. By making the pulse width sufficiently smaller than the pulse repetition period, the temporal waveform of the optical power can be measured with sufficiently high spatial resolution relative to the entire length of the optical fiber.

[0139] Next, the operation of the measuring apparatus 1A, 1B, or 1C according to the present embodiment will be described, and the inter-core crosstalk measuring method according to the present embodiment using the measuring apparatus 1A, 1B, or 1C will be described. Figure 16 This is a flowchart showing the inter-core crosstalk measurement method according to this embodiment.

[0140] First, as step ST1, a light reflecting surface is formed or provided at the second end portion 10b. Examples of the light reflecting surface are as follows: Figures 8 to 10 That is, step ST1 may also include providing a reflective film 71 on the end face 11a of the glass fiber 11 (see Figure 8 ) or the reflective member 72 (refer to Figure 9 ), or immersing the end face 11a in liquid metal 74 (refer to Figure 10 ) step ST11.

[0141] Next, as step ST2, the test light is made incident from the light source unit 20A or 20B at the first end portion 10a into any one of the cores 13a, 13b, 13c, and 13d (the first spatial channel or the first core, here, the core 13a is used as an example). Figure 1 、 Figure 4 ), the test light is made incident on the core 13a by switching the first optical switch 22. The first optical switch 22 can be switched according to a control signal from the operation unit 60 or manually. Figure 5 ), the test light is made incident from the light source 23 corresponding to the core 13a among the light sources 23, 24, 25, and 26.

[0142] Next, as step ST3 , at least a portion of the test light is reflected on the light reflecting surface of the second end portion 10 b .

[0143] Then, part of the light reflected on the light reflecting surface is emitted from the core 13a, and the other part is emitted from a core different from the core 13a (the second spatial channel or the second core, here, the cores 13b, 13c, and 13d, respectively) due to inter-core crosstalk. In step ST4, the first optical power is detected, and the second optical power is detected. The first optical power is the power of the light emitted from the core 13a, and the second optical power is the power of the light emitted from the cores 13b, 13c, and 13d, respectively. At this time, in the light detection unit 30A (refer to Figure 1 、 Figure 5 ), the light from the cores 13a, 13b, 13c, and 13d is sequentially incident on the optical receiver 31 by switching the second optical switch 32. The second optical switch 32 can be switched according to a control signal from the operation unit 60 or manually. Figure 4 ), the light from the cores 13a, 13b, 13c, and 13d is respectively incident on the optical receivers 33, 34, 35, and 36 corresponding to the cores 13a, 13b, 13c, and 13d.

[0144] The first optical power is the sum of the optical power components emitted from the core 13a (first spatial channel) of the return optical power components of the test light, including backscattered light at each position in the longitudinal direction of the MCF 10. The second optical power is the sum of the optical power components emitted from the cores 13b, 13c, and 13d (second spatial channels) of the return optical power components of the test light, including backscattered light at each position in the longitudinal direction of the MCF 10.

[0145] Next, as step ST5, the magnitude of the crosstalk between core 13a and cores 13b, 13c, and 13d is calculated in calculation unit 60 based on the first optical power and the second optical power. At this time, the magnitude of the crosstalk XT between core 13a and cores 13b, 13c, and 13d is calculated based on the first optical power PW1 and the second optical power PW2 according to the following mathematical formula (1).

[0146]

[0147] When measuring first optical power PW1, the power of light emitted from core 13a is measured at first end 10a. The light emitted from core 13a includes not only light reflected from the light-reflecting surface of second end 10b, but also backscattered light generated when the test light incident on any of cores 13a, 13b, 13c, and 13d at first end 10a propagates along the longitudinal direction of MCF 10, as well as return light (noise light) such as unintended reflections generated outside the light-reflecting surface. Similarly, when measuring second optical power PW2, the power of light emitted from each of cores 13b, 13c, and 13d is measured at first end 10a. At this time, the light emitted from the fiber cores 13b, 13c, and 13d respectively includes not only the light reflected on the light reflecting surface of the second end 10b, but also the backscattered light generated when the test light incident on any one of the fiber cores 13a, 13b, 13c, and 13d at the first end 10a propagates along the length direction in the MCF10, and the return light (noise light) such as the unexpected reflected light generated outside the light reflecting surface.

[0148] The first cores (first spatial channels) into which the test light is incident are set as cores 13a, 13b, 13c, and 13d, and the above-mentioned steps ST2 to ST5 are repeated in sequence.

[0149] Figure 17 FIG. 1 is a flowchart showing a modified example of the method for measuring crosstalk between cores. In this modified example, the step ST1 of forming or setting the light reflecting surface at the second end portion 10b includes a step ST12 instead of the above-mentioned step ST11. In step S12, as shown in FIG. Figure 11 As shown, the second end surface of the MCF 81 is connected to the end surface 11 a of the MCF 10 at the second end portion 10 b , wherein the first end surface 81 a of the MCF 81 is provided with a reflective film 82 serving as a light reflecting surface.

[0150] Figure 18 FIG. 1 is a flow chart showing another modified example of the method for measuring crosstalk between cores. In this modified example, the step ST1 of forming or setting the light reflecting surface at the second end portion 10b includes a step ST13 instead of the above-mentioned step ST11. In step ST13, as shown in FIG. Figure 12 As shown, the second end faces of the plurality of SCFs 92 are optically coupled to the cores 13a, 13b, 13c, and 13d at the second end portion 10b, respectively. The first end face 92a of the SCF 92 is provided with a reflective film 93 serving as a light reflecting surface.

[0151] Figure 19 FIG. 1 is a flow chart showing another modified example of the method for measuring crosstalk between cores. In this modified example, the step ST1 of forming or setting the light reflecting surface at the second end portion 10b includes a step ST14 instead of the above-mentioned step ST11. In step ST14, as shown in FIG. Figure 6 or Figure 7 As shown, the end face 11a of the glass fiber 11 is formed into a flat surface or a curved surface by grinding or cutting, and these are used as light reflecting surfaces. Alternatively, the substantially flat end face 11a that has only been cut may be used as a light reflecting surface.

[0152] Effects obtained by the above-described measuring devices 1A, 1B, and 1C and the inter-core crosstalk measuring method according to the present embodiment will be described. Figure 27 It is a diagram schematically showing the structure of a measuring device 200 according to a reference example. Figure 27 The illustrated measuring device 200 is used to measure inter-core crosstalk in an MCF 10. It includes a single light source 201, a first optical switch 202, a FIFO 203, a FIFO 204, a second optical switch 205, and a single optical receiver 206. Light source 201, first optical switch 202, and FIFO 203 are connected to first end 10a of the MCF 10. FIFO 204, second optical switch 205, and optical receiver 206 are connected to second end 10b of the MCF 10. Test light output from light source 201 enters a first core (first spatial channel) selected by first optical switch 202 among the multiple cores of the MCF 10 at first end 10a. At second end 10b, second optical switch 205 sequentially selects the first core into which the test light enters and a second core (second spatial channel) different from the first core. Optical receiver 206 detects the optical power of the test light propagating through the first core and the optical power of the crosstalk light propagating through the second core. The inter-core crosstalk is calculated based on these optical powers.

[0153] exist Figure 27 In the illustrated measurement device 200, test light is injected into the first core at the first end 10a of the MCF 10, and the power of the test light emitted from the first and second cores is detected at the second end 10b of the MCF 10. However, when the MCF 10 to be measured is installed, it may be difficult to connect the unit consisting of the light source 201, the first optical switch 202, and the FIFO 203 to the first end 10a of the MCF 10, and to connect the unit consisting of the FIFO 204, the second optical switch 205, and the optical receiver 206 to the second end 10b of the MCF 10, which is farther away from the first end 10a.

[0154] In the measuring devices 1A, 1B, and 1C and the measuring method according to the present embodiment, it is sufficient to connect the light source unit 20A or 20B and the light detection unit 30A or 30B to the first end 10a of the MCF 10, and it is not necessary to connect any of them to the second end 10b. Therefore, even in the case of an MCF 10 where the first end 10a and the second end 10b are more than a few kilometers apart, the light source unit 20A or 20B and the light detection unit 30A or 30B can be easily connected to the MCF 10. In addition, in the measuring devices 1A, 1B, and 1C and the measuring method according to the present embodiment, the magnitude of the crosstalk is calculated based on the power of the light reflected on the light reflecting surface provided (or formed) at the second end 10b. The power of the light reflected on the light reflecting surface is significantly greater than the power of the backward Rayleigh scattered light. Therefore, even when the crosstalk is small, the detection signal will not be overwhelmed by the noise, and the crosstalk between the cores can be appropriately measured.

[0155] As described above, the light reflecting surface may be configured to reflect at least a portion of the test light with a reflectivity of 0.001 or greater. In this case, by setting the first optical power PW1 and the second optical power PW2 to sufficient levels, the error in the measurement results caused by backscattering can be reduced, thereby improving the accuracy of inter-core crosstalk measurement.

[0156] As described above, the light reflecting surface may be the end surface 11a of the MCF 10, and step ST1 may include step ST11 of providing a reflective film 71 or a reflective member 72 on the end surface 11a, or immersing the end surface 11a in liquid metal 74. This can increase the reflectivity of the light reflecting surface, further increasing the first optical power PW1 and the second optical power PW2, and thus enabling more accurate crosstalk measurement.

[0157] As described above, measurement devices 1A, 1B, and 1C may include an MCF 81 having a reflective film 82 as a light-reflecting surface provided on a first end face 81a. The second end face of the MCF 81 may be connected to the end face 11a of the MCF 10 at its second end 10b. Similarly, in the measurement method, step ST1 may include step ST12 of connecting the second end face of the MCF 81 at its second end 10b to the end face 11a of the MCF 10, wherein the first end face 81a of the MCF 81 is provided with the reflective film 82 as a light-reflecting surface. These measurement devices 1A, 1B, and 1C and measurement methods can improve the reflectivity of the light-reflecting surface, further increasing the first optical power PW1 and the second optical power PW2, thereby enabling more accurate crosstalk measurement. Furthermore, since a light-reflecting film is not provided on the end face 11a of the MCF 10, the MCF 81 need only be connected to the end face 11a of the MCF 10, thereby simplifying the measurement process.

[0158] As described above, the measuring devices 1A, 1B, and 1C may include the same number of SCFs 92 as the cores 13a, 13b, 13c, and 13d, each having a reflective coating 93 provided on the first end face 92a as a light-reflecting surface. The second end face of each SCF 92 is optically coupled to the cores 13a, 13b, 13c, and 13d at the second end portion 10b. Similarly, in the measuring method, step ST1 may include a step ST13 of optically coupling the second end face of each SCF 92, each having a reflective coating 93 provided on the first end face 92a as the light-reflecting surface as the cores 13a, 13b, 13c, and 13d at the second end portion 10b. These measuring devices 1A, 1B, and 1C and their measuring methods improve the reflectivity of the light-reflecting surface, further increasing the first optical power PW1 and the second optical power PW2, thereby enabling more accurate crosstalk measurement. Furthermore, since a light reflecting film is not provided on the end surface 11 a of the MCF 10 , it is sufficient to connect optical components such as the FIFO 91 to the end surface 11 a of the MCF 10 , thereby facilitating measurement work.

[0159] As described above, in the measuring devices 1A, 1B, and 1C, the first end surface 11a of the MCF 10 may be used as a light reflecting surface. This eliminates the need for special devices such as the reflection enhancing devices 80 and 90, and simplifies the structure of the measuring device.

[0160] As in this embodiment, the measurement devices 1A, 1B, and 1C may include optical circulators 41, 42, 43, and 44 and a FIFO 50. The optical circulators 41, 42, 43, and 44 have a first port P1, a second port P2, and a third port P3. Light input to the first port P1 is output from the second port P2, and light input to the second port P2 is output from the third port P3. The FIFO 50 optically couples the fiber cores 13a, 13b, 13c, and 13d in the first end portion 10a of the MCF 10 to the second port P2 of each optical circulator 41, 42, 43, and 44, respectively. The light source unit 20A or 20B is optically coupled to the first port P1 of the optical circulator 41, 42, 43, and 44. The light detection unit 30A or 30B is optically coupled to the third port P3 of the optical circulator 41, 42, 43, and 44. This makes it possible to easily realize a structure in which test light from the light source unit 20A or 20B is incident on the cores 13a, 13b, 13c, and 13d, respectively, and the light detector 30A or 30B detects light emitted from the core into which the test light is incident and light emitted from other cores.

[0161] like Figure 5As in the measurement device 1C shown in FIG. 1 , the light source unit 20B may include the same number of light sources 23, 24, 25, and 26 as the cores 13a, 13b, 13c, and 13d, and the light sources 23, 24, 25, and 26 may be optically coupled to the first ports P1 of the optical circulators 41, 42, 43, and 44, respectively. This allows the input of test light to the first ports P1 of the optical circulators 41, 42, 43, and 44, respectively, with a simple configuration.

[0162] like Figure 1 As in the measurement device 1A shown, the light source unit 20A may include a single light source 21 and a first optical switch 22 that selectively optically couples the single light source 21 to the first port P1 of any one of the optical circulators 41, 42, 43, and 44. This can reduce the number of light sources.

[0163] like Figure 4 As in the measurement device 1B shown in FIG. 1 , the light detection unit 30B may include the same number of optical receivers 33, 34, 35, and 36 as the cores 13a, 13b, 13c, and 13d, and the optical receivers 33, 34, 35, and 36 may be optically coupled to the third ports P3 of the optical circulators 41, 42, 43, and 44, respectively. This allows detection of light output from the third ports P3 of the optical circulators 41, 42, 43, and 44, respectively, with a simple configuration.

[0164] like Figure 1 As in the measurement device 1A shown, the light detection unit 30A may include a single light receiver 31 and a second optical switch 32 that selectively optically couples the single light receiver 31 to the third port P3 of any one of the optical circulators 41, 42, 43, and 44. This can reduce the number of light receivers.

[0165] Alternatively, the inter-core crosstalk of FIFO 50 may be 0.259 times or less, 0.122 times or less, 0.047 times or less, or 0.023 times or less of the inter-core crosstalk of MCF 10. Consequently, the inter-core crosstalk measurement error of MCF 10 caused by the inter-core crosstalk of FIFO 50 can be reduced to 1 dB or less, 0.5 dB or less, 0.2 dB or less, or 0.1 dB or less, respectively, allowing the inter-core crosstalk of MCF 10 to be measured with higher accuracy.

[0166] Here, we describe the crosstalk measurement error in the measurement devices 1A, 1B, and 1C and the measurement method of this embodiment. In addition to light reflected from the light-reflecting surface, backscattered Rayleigh light also enters the light detection unit 30A (30B). If the first optical power PW1 and the second optical power PW2 become too low due to factors such as low reflectivity of the light-reflecting surface or excessive transmission loss due to an excessively long MCF 10, the difference between the first and second optical powers PW1 and PW2 and the backscattered Rayleigh light power decreases, reducing the accuracy of inter-core crosstalk measurement.

[0167] The inventors of the present disclosure have found that when the light reflecting surface is the end surface 11a of the MCF 10 (see Figure 6 and Figure 7 ), in the measurement of continuous light or chopped light, the measurement error ΔXT of the inter-core crosstalk caused by backscattering Rayleigh is expressed in decibels. dB [dB] is expressed by the following mathematical formula (2).

[0168]

[0169] Where, λ is the wavelength of the test light (μm), π is the circumference, n is the refractive index of the cores 13a, 13b, 13c, and 13d of the MCF 10, and α R is the Rayleigh scattering loss coefficient of the cores 13a, 13b, 13c, and 13d (km -1 ), α is the transmission loss coefficient of the cores 13a, 13b, 13c, and 13d (km -1 ), w is 0.5 times the mode field diameter of the cores 13a, 13b, 13c, and 13d (μm), φ is the angle (rad) formed by the imaginary plane H2 (or H2a) that touches the centers of the cores 13a, 13b, 13c, and 13d on the end face 11a and the imaginary plane H1 that is orthogonal to the central axis AX of the MCF 10, L is the length of the MCF 10 (km), and A eff is the effective cross-sectional area of ​​the cores 13a, 13b, 13c, and 13d (μm 2 ). However, when the refractive indices of two or more cores among the cores 13a, 13b, 13c, and 13d are different from each other, n is the average of the refractive indices of the cores 13a, 13b, 13c, and 13d. Similarly, when the Rayleigh scattering loss coefficients of two or more cores among the cores 13a, 13b, 13c, and 13d are different from each other, α Ris the average value of the Rayleigh scattering loss coefficients of cores 13a, 13b, 13c, and 13d. If the transmission loss coefficients of two or more of cores 13a, 13b, 13c, and 13d differ from each other, α is the average value of the transmission loss coefficients of cores 13a, 13b, 13c, and 13d. If the mode field diameters of two or more of cores 13a, 13b, 13c, and 13d differ from each other, w is 0.5 times the average value of the mode field diameters of cores 13a, 13b, 13c, and 13d. If the angle between imaginary plane H2 and imaginary plane H1 differs for two or more of cores 13a, 13b, 13c, and 13d, φ is the average value of the angles for cores 13a, 13b, 13c, and 13d. When the effective cross-sectional areas of two or more cores among the cores 13a, 13b, 13c, and 13d are different from each other, A eff is the average value of the effective cross-sectional area of ​​the cores 13a, 13b, 13c, and 13d. R , α, and w are the values ​​at wavelength λ.

[0170] The average value of the transmission loss of the cores 13a, 13b, 13c, and 13d is represented by α dB L(dB). α dB (dB·km -1 ) is obtained by dividing the average value of the transmission loss coefficient α(km -1 ) is the value obtained by multiplying 10 / ln(10)(≈4.34). In addition, φ(rad) expressed in radians can be converted to θ(degrees) in degrees (θ=180φ / π). eff The average value is 110μm 2 The average value of w is 0.5·(A eff / π), and the average value of n is 1.444, the measurement error of the inter-core crosstalk caused by backscattering varies with the angle θ (degrees) as shown in the following figure: Figure 20 shown. Figure 20 The figure shows the measurement error of the inter-core crosstalk caused by Rayleigh backscattering and the transmission loss α when the angle θ is changed by 1 degree from 0 to 6. dB L(dB) relationship. Figure 20 In the figure, the vertical axis represents the measurement error, and the horizontal axis represents the transmission loss α dB L (dB) In addition, the curves G51 to G57 show the cases where the angle θ is 0 degree, 1 degree, 2 degrees, 3 degrees, 4 degrees, 5 degrees, and 6 degrees, respectively.

[0171] Reference Figure 20 It can be seen that when the angle θ is less than 2 degrees, the measurement error becomes significantly smaller.dB The relationship between L and the measurement error of the inter-core crosstalk caused by backscattering is expressed as the maximum permissible transmission loss α when the permissible measurement error is set to 10 dB, 5 dB, 2 dB, 1 dB, 0.5 dB, 0.2 dB, and 0.1 dB. dB Rearranging the relationship between L (dB) and angle θ (degrees) yields Figure 21 . Figure 21 The maximum permissible transmission loss α is shown when the permissible measurement error is 2 dB, 1 dB, 0.5 dB, 0.2 dB, or 0.1 dB. dB A graph showing the relationship between L (dB) and angle θ (degrees). Figure 21 The vertical axis represents the maximum permissible transmission loss α dB L (dB), the horizontal axis represents the angle θ (degrees). In addition, curves G61 to G65 represent the cases where the allowable measurement errors are 2dB, 1dB, 0.5dB, 0.2dB and 0.1dB respectively. Figure 21 In the experiment, according to the allowable measurement error, the transmission loss α dB L needs to be in the range below the corresponding curve. The value of formula (2) is 10 0.2 Hereinafter, the crosstalk measurement error caused by Rayleigh backscattered light can be reduced to 2 dB or less.

[0172] If PW1, measured with a high level of noise due to Rayleigh backscattered light, is defined as PW10, and PW2, measured with a high level of noise due to Rayleigh backscattered light, is defined as PW20, then the magnitude XT of the crosstalk between the core 13a and the cores 13b, 13c, and 13d can be calculated using the following mathematical formula (3). In this case, the crosstalk measurement error due to Rayleigh backscattered light can be suppressed, allowing for more accurate crosstalk measurement.

[0173]

[0174] When a light reflecting surface is formed or provided with the goal of φ=0 (rad), the magnitude XT of crosstalk between the core 13a and the cores 13b, 13c, and 13d is calculated by the following formula (4) based on PW10 and PW20.

[0175]

[0176] Here, the wavelength λ and the effective cross-sectional area A are eff changes, it can be seen that the longer the wavelength λ is, the greater the effective cross-sectional area A is. eff The smaller the angle θ and the transmission loss α dB The smaller the value range allowed between L, the narrower the effective cross-sectional area A. eff Indicated as Aeff =kπw 2 k is a constant, 0.95≤k≤1.1. According to the research of the inventors of this disclosure, the smaller the constant k is, the greater the difference between the angle θ and the transmission loss α. dB The narrower the range of values ​​allowed for L.

[0177] According to the wavelength λ of 1.625μm and the effective cross-sectional area A eff 60μm 2 , the constant k is 0.95. The results show that when the wavelength λ is less than 1.625μm and the effective cross-sectional area A eff 60μm 2 In the above case, the angle θ and the transmission loss α dB L satisfies the ratio Figure 20 The following mathematical formula (5) or (6) can be used for the range below the curve G41. This makes it possible to reduce the measurement error of the inter-core crosstalk caused by the backscattered Rayleigh light to 10 dB or less, thereby measuring the inter-core crosstalk with higher accuracy.

[0178] α dB ≤1.58×10+3.23×10 -2 θ-4.95×10 -1 θ 2 …(5)

[0179] α dB L≤a0+a1θ+a2θ 2 …(6)

[0180] a0=-3.40×10 -1 [dB], a1=-3.73×10 -2 [dB / degree],a2=7.46×10 0 [dB / degree 2 ]

[0181] When the wavelength λ is less than 1.625 μm and the effective cross-sectional area A eff 60μm 2 In the above case, the angle θ and the transmission loss α dBL can satisfy the following mathematical formula (7) representing the range below curve G42, the following mathematical formula (8) representing the range below curve G43, the following mathematical formula (9) representing the range below curve G44, the following mathematical formula (10) representing the range below curve G45, the following mathematical formula (11) representing the range below curve G46, and the following mathematical formula (12) representing the range below curve G47. Thus, the measurement error of the inter-core crosstalk caused by backscattered Rayleigh light can be reduced to 5 dB or less, 2 dB or less, 1 dB or less, 0.5 dB or less, 0.2 dB or less, and 0.1 dB or less, respectively, thereby enabling the inter-core crosstalk to be measured with higher accuracy.

[0182] α dB L≤1.22×10+6.70×10 -3 θ-4.99×10 -1 θ 2 …(7)

[0183] α dB L≤8.81-1.12×10 -2 θ-4.91×10 -1 θ 2 …(8)

[0184] α dB L≤6.70-2.73×10 -2 θ-4.60×10 -1 θ 2 …(9)

[0185] α dB L≤4.84-6.47×10 -2 θ-3.89×10 -1 θ 2 …(10)

[0186] α dB L≤2.83-9.90×10 -2 θ-2.56×10 -1 θ 2 …(11)

[0187] α dB L≤1.72-9.04×10 -2 θ-1.61×10 -1 θ 2 …(12)

[0188] Due to the measurement error of the inter-core crosstalk caused by backward Rayleigh scattering, the measured value of the inter-core crosstalk is larger than the true value of the inter-core crosstalk. Therefore, if the measured value of the inter-core crosstalk is smaller than the upper limit of the specification of the inter-core crosstalk, it is ensured that the true value of the inter-core crosstalk is smaller than the upper limit of the specification of the inter-core crosstalk. However, as described above, the measurement error of the inter-core crosstalk caused by backward Rayleigh scattering varies according to the reflectivity of the light reflecting surface of the second end 10b. In addition, in fact, the reflectivity of the light reflecting surface depends on the state of the light reflecting surface at each measurement. Therefore, the measurement error of the inter-core crosstalk caused by backward Rayleigh scattering varies within a certain range managed in advance (for example, the above-mentioned range of less than 10dB, less than 5dB, less than 2dB, less than 1dB, less than 0.5dB, less than 0.2dB or less than 0.1dB) at each measurement. For this reason, the angle θ and the transmission loss α are selected so that the upper limit of the measurement error of the inter-core crosstalk caused by backward Rayleigh scattering can be suppressed to a lower level. dB The measurement can be performed within the range of L.

[0189] Next, the test light is Figure 15 The case of pulsed light is described below. Figure 22 This is a graph schematically showing the time waveforms of the power of light emitted from the first core (here, assumed to be core 13a) into which the test light is incident (curve G21), and the power of light emitted from the second core (here, cores 13b, 13c, and 13d, respectively) (curve G22) when the test light is pulsed light. Figure 22 In the figure, the vertical axis represents optical power (logarithmic scale), and the horizontal axis represents the delay time after the test light is incident. The delay time is proportional to the distance from the first end 10a. Specifically, it is equal to the value obtained by dividing twice the distance from the first end 10a by the group velocity of the pulsed light in the MCF 10.

[0190] When pulsed test light is incident on core 13a at first end 10a of MCF 10, backscattered Rayleigh light is emitted from cores 13a, 13b, 13c, and 13d at first end 10a during a period T1 until at least a portion of the test light, reflected by the light-reflecting surface at second end 10b, returns to first end 10a. The optical power of this backscattered Rayleigh light gradually decreases over time (in other words, as the pulsed light travels within core 13a). After a certain period of time, the power of the light emitted from cores 13b, 13c, and 13d becomes so weak that it falls below the detection limit of the optical receiver (indicated by the dashed line D in the figure), making it undetectable.

[0191] Then, at least a portion of the test light reflected by the light-reflecting surface of second end portion 10b returns to first end portion 10a after a delay time equal to twice the distance between first end portion 10a and the light-reflecting surface has elapsed since the test light entered core 13a. At this point, as shown by curve G21, the power of the light emitted from core 13a increases instantaneously (waveform E1 in the figure). As shown by curve G22, the power of the light emitted from cores 13b, 13c, and 13d also increases instantaneously (waveform E2 in the figure). The peak values ​​of these waveforms E1 and E2 are used as the first optical power PW1 and the second optical power PW2, respectively, for calculating inter-core crosstalk.

[0192] As such, the first optical power PW1 and the second optical power PW2 may be the powers of light emitted from the first and second cores, respectively, after the test light is incident on the first core and a delay time equivalent to twice the distance between the first end portion 10a and the light reflecting surface has elapsed. This eliminates the influence of Rayleigh backscattered light from the first and second optical powers PW1 and PW2, allowing for more accurate measurement of inter-core crosstalk.

[0193] In the above-described measurement method using pulsed light as the test light, when the light reflecting surface is the end face 11a of the MCF 10, the ratio of the power A1 of the pulsed light reflected on the light reflecting surface (i.e., the first optical power PW1 and the second optical power PW2) to the power A2 of the pulsed light generated immediately before the reflection, excluding Rayleigh backscattered light of the reflected light, is calculated using the following mathematical formula (13) (the gain of the signal light due to reflection, G = A1 / A2). Here, T is the pulse width (km) of the test light propagating through the core of the MCF 10.

[0194]

[0195] By setting the value G to 10 or more, the gain G of the signal light due to the reflection can be set to 10 dB or more, thereby enabling the measurement of the inter-core crosstalk with higher accuracy. 2 Above, 10 3 Above or 10 4 As described above, the gain G of the signal light due to the reflection can be set to 20 dB or more, 30 dB or more, or 40 dB or more, respectively, thereby enabling the inter-core crosstalk to be measured with higher accuracy.

[0196] [First Modification]

[0197] A first modified example of the above embodiment will be described. Figure 23 100A is a diagram showing the appearance of a holding unit 100A included in a measurement device according to a first modification. Figure 23Part (a) is a plan view of the holding portion 100A. Figure 23 Part (b) is a side view of the holding portion 100A. Figure 23 Part (c) is a front view of the holder 100A. The holder 100A holds the MCF 10 so that its end surface 11a is in contact only with gas (e.g., air) or vacuum. In other words, the holder 100A holds the MCF 10 so that its end surface 11a is not in contact with anything other than gas or vacuum. At the end of the MCF 10, including the end surface 11a, the coating resin 12 is removed, exposing the glass fiber 11. No reflective film or reflection enhancing device is provided on the end surface 11a.

[0198] The holding unit 100A includes a flat table 101A and a cover 102. The flat table 101A is a plate-shaped component, made of metal or resin, for example. A V-groove 103 extending in one direction is formed on the main surface of the flat table 101A. The MCF 10 is accommodated in the V-groove 103 in the portion having the coating resin 12. Furthermore, the cover 102, positioned opposite the main surface of the flat table 101A, covers the MCF 10. As a result, the MCF 10 is held within the area defined by the V-groove 103 and the cover 102, with its end surface 11a suspended.

[0199] Figure 24 10 is a diagram showing the appearance of a holding portion 100B capable of holding a tape core wire 10A including a plurality of MCFs 10 . Figure 24 Part (a) is a plan view of the holding portion 100B. Figure 24 Part (b) is a side view of the holding portion 100B. Figure 24 Part (c) is a front view of the holding unit 100B. The tape core wire 10A has a coating resin 16. The coating resin 16 covers the multiple MCFs 10 so that they are aligned in a row and secures the multiple MCFs 10 to one another. The holding unit 100B holds the tape core wire 10A so that the end surfaces 11a of the multiple MCFs 10 are in contact only with gas (e.g., air) or vacuum. In other words, the holding unit 100B simultaneously holds the multiple MCFs 10 so that the end surfaces 11a of the multiple MCFs 10 are not in contact with anything other than gas or vacuum.

[0200] The holding portion 100B includes a flat table 101B and a cover 102. The flat table 101B is a plate-shaped member similar to the flat table 101A and can be made of, for example, metal or resin. A plurality of V-grooves 103 extending in one direction are formed on the main surface of the flat table 101B. The plurality of MCFs 10 with core wires 10A are housed in the V-grooves 103 in the portions having the coating resins 12 and 16, respectively. Furthermore, the cover 102, which is arranged so as to face the main surface of the flat table 101B, covers the core wires 10A. Thus, the plurality of MCFs 10 are held in a state where the end faces 11a are suspended in the area defined by the plurality of V-grooves 103 and the cover 102.

[0201] As in this modified example, the measuring devices 1A, 1B, and 1C may further include a holding portion 100A (a holding portion 100B when a plurality of MCFs 10 constitute the cored wire 10A) that holds the MCF 10 so that the end surface 11a is in contact only with gas or vacuum. Figure 16 The measurement method shown in FIG1 includes a step of placing the end face 11a in contact only with gas or vacuum instead of step ST11. This improves the reflectivity of the light reflecting surface, further increasing the first optical power PW1 and the second optical power PW2, and allowing more accurate measurement of inter-core crosstalk.

[0202] Figure 25 This figure schematically illustrates a cross-section of a dust cover 105 that houses the holding unit 100A (or 100B). The dust cover 105 includes a mounting platform 104 and an openable and closable lid 106. The holding unit 100A (or 100B) is housed within the dust cover 105 and placed on the mounting platform 104, where it is supported at a higher position. Figure 26 106 is an open state. The MCF 10 is set on the holding portion 100A (or 100B) with the cover 106 open. After the MCF 10 is set, the cover 106 is closed.

[0203] In this manner, by covering the end face 11a of the MCF 10 held by the holding portion 100A (or 100B) with the dust cover 105, the possibility of dust in the gas adhering to the end face 11a can be reduced, and the light reflectivity of the end face 11a can be stably maintained. In addition, by raising the position of the end face 11a of the MCF 10 using the mounting table 104, the possibility of dust on the bottom surface of the dust cover 105 adhering to the end face 11a can be reduced, thereby maintaining the light reflectivity of the end face 11a more stably.

[0204] [Second Modification]

[0205] In the above embodiment, the reflectance of the light-reflecting surfaces of cores 13a, 13b, 13c, and 13d of MCF 10 is described as being equal. However, the reflectance of the light-reflecting surfaces of cores 13a, 13b, 13c, and 13d may differ. Such differences in reflectance are typically caused by differences in angle φ between cores 13a, 13b, 13c, and 13d. For example, if the reflectance of the light-reflecting surfaces of cores 13a and 13b differs, inter-core crosstalk is measured by injecting test light into core 13a (i.e., using core 13a as the first core). Subsequently, inter-core crosstalk is measured by injecting test light into core 13b (i.e., using core 13b as the first core). The geometric mean of the two inter-core crosstalk values ​​(linear values) measured is then used as the final inter-core crosstalk measurement value. This reduces measurement errors caused by differences in reflectance.

[0206] At this time, if the absolute value of the decibel value of the reflectivity ratio between the cores 13a, 13b, 13c, and 13d is 15.8 dB or less, 9.0 dB or less, 6.1 dB or less, 4.2 dB or less, 2.7 dB or less, or 1.9 dB or less, the measurement error caused by the difference in reflectivity can be suppressed to 5 dB or less, 2 dB or less, 1 dB or less, 0.5 dB or less, 0.2 dB or less, or 0.1 dB or less, respectively. For example, the absolute value of the decibel value of the reflectivity ratio is calculated by the following mathematical formula (14). Wherein w1 is 0.5 times the mode field diameter of the core into which the test light is incident, w2 is 0.5 times the mode field diameter of a core different from the core into which the test light is incident, φ1 is the angle φ of the core into which the test light is incident, and φ2 is the angle φ of the core different from the core into which the test light is incident.

[0207]

[0208] The method for measuring spatial crosstalk between channels, the method for measuring inter-core crosstalk between multi-core optical fibers, the device for measuring spatial crosstalk between channels, and the device for measuring inter-core crosstalk between multi-core optical fibers disclosed herein are not limited to the above-described embodiments and variations thereof, and various variations are possible. For example, the above-described variations may be combined with one another based on the desired purpose and effect. Furthermore, the configuration of the light-reflecting surface in the second end portion 10b of the MCF 10 is not limited to the above-described embodiment. The number of cores in the MCF 10 is also not limited to the above-described embodiment.

[0209] Description of Reference Numerals

[0210] 1A, 1B, 1C measuring devices

[0211] 10 Multi-core Fiber (MCF)

[0212] 10a first end

[0213] 10A core wire

[0214] 10b Second end

[0215] 11. Fiberglass

[0216] 11a End face

[0217] 12 Coating resin

[0218] 13a, 13b, 13c, 13d fiber cores

[0219] 14 Cladding

[0220] 15 Mark

[0221] 16 Coating resin

[0222] 20A, 20B light source

[0223] 21, 23, 24, 25, 26 light sources

[0224] 22 First Optical Switch

[0225] 22a Input port

[0226] 22b, 22c, 22d, 22e output ports

[0227] 30A, 30B Light detection unit

[0228] 31, 33, 34, 35, 36 Optical receivers

[0229] 32 Second optical switch

[0230] 32a output port

[0231] 32b, 32c, 32d, 32e input ports

[0232] 40 Circulator

[0233] 41, 42, 43, 44 Light Circulator

[0234] 50 fan-in fan-out (FIFO)

[0235] 50a, 50b, 50c, 50d, 50e input and output ports

[0236] 60 Operation unit

[0237] 71 reflective film

[0238] 72 reflective components

[0239] 73 Container

[0240] 74 Liquid Metal

[0241] 80 Reflection Enhancement Device

[0242] 81 MCF

[0243] 82 reflective film

[0244] 90 Reflection Enhancement Device

[0245] 91FIFO

[0246] 92 Single Core Fiber (SCF)

[0247] 93 reflective film

[0248] 100A, 100B holding portion

[0249] 101A, 101B flat table

[0250] 102 cover

[0251] 103 V-slot

[0252] 104 loading platform

[0253] 105 dust cover

[0254] 106 cover

[0255] 131 end face

[0256] 200 measuring device

[0257] 201 Light Source

[0258] 202 First Optical Switch

[0259] 203, 204 FIFO

[0260] 205 Second Optical Switch

[0261] 206 optical receiver

[0262] AX center axis

[0263] E1 and E2 waveforms

[0264] G21, G22, G51 to G57, G61 to G65 curves

[0265] H1, H2, H2a imaginary planes

[0266] L1, L2 light P1 First port P2 Second port P3 Third port PW1 First optical power PW2 Second optical power ST1, ST2, ST3, ST4, ST5, ST11, ST12, ST13 During step T1

[0267] φ angle.

Claims

1. A method for measuring spatial crosstalk between channels, comprising measuring the spatial crosstalk between channels of a space-division multiplexing optical system, wherein the space-division multiplexing optical system comprises a first input / output portion and a second input / output portion opposite to the first input / output portion, and comprises a first spatial channel and a second spatial channel, the method comprising: The first step is to form or set a light reflecting surface on the second incident and output portion; In a second step, the test light is made incident on the first spatial channel at the first incident and output portion; A third step is to reflect at least a portion of the test light on the light reflecting surface; In a fourth step, a first optical power and a second optical power are detected, where the first optical power is the power of light in the at least a portion of the light that is emitted from the first spatial channel at the first input / output portion, and the second optical power is the power of light in the at least a portion of the light that is emitted from the second spatial channel at the first input / output portion. as well as In a fifth step, based on the first optical power and the second optical power, a magnitude of crosstalk between the first spatial channel and the second spatial channel is calculated.

2. The method for measuring spatial channel crosstalk according to claim 1, wherein: The first optical power is the sum of optical power components emitted from the first spatial channel in the return optical power components of the test light including backscattered light at each position in the longitudinal direction of the space-division multiplexing optical system. The second optical power is the sum of optical power components emitted from the second spatial channel among return optical power components of the test light including backscattered light at respective positions in the longitudinal direction of the space-division multiplexing optical system.

3. The method for measuring spatial channel crosstalk according to claim 2, wherein: The space division multiplexing optical system is a space division multiplexing optical fiber, The light reflecting surface is the end face of the space division multiplexing optical fiber, When the wavelength of the test light is λ (μm), the circumference is π, the refractive index of the first spatial channel and the second spatial channel of the space-division multiplexing optical fiber is n, and the transmission loss coefficient of the first spatial channel and the second spatial channel is α (km -1 ), 0.5 times the mode field diameter of the first spatial channel and the second spatial channel is set to w (μm), the angle formed by the plane on the end face that touches the center of the first spatial channel and the second spatial channel and the plane that is orthogonal to the central axis of the spatial division multiplexing optical fiber is set to φ (rad), the length of the spatial division multiplexing optical fiber is set to L (km), the effective cross-sectional area of ​​the first spatial channel and the second spatial channel is set to A eff (μm 2 ), setting the Rayleigh scattering loss coefficient of the first spatial channel and the second spatial channel to α R (km -1 ), the value of the mathematical formula (A) is 10 0.2 the following, When the first optical power is set to PW1, the second optical power is set to PW2, and the magnitude of the crosstalk between the first spatial channel and the second spatial channel is set to XT, mathematical formula (B) is used to calculate XT.

4. The method for measuring spatial channel crosstalk according to claim 2, wherein: The space division multiplexing optical system is a space division multiplexing optical fiber, The light reflecting surface is the end face of the space division multiplexing optical fiber, The angle formed by the plane touching the centers of the first spatial channel and the second spatial channel on the end face and the plane perpendicular to the central axis of the space division multiplexing optical fiber is θ (degrees), and the loss coefficients of the first spatial channel and the second spatial channel are α dB (dB·km -1 ), when the length of the space division multiplexing optical fiber is set to L (km), the angle θ and the transmission loss α dB L satisfies mathematical formula (C), the wavelength of the test light is less than 1.625 μm, and the effective cross-sectional area of ​​the first spatial channel and the second spatial channel at the wavelength is 60 μm 2 above, When the first optical power is set to PW1, the second optical power is set to PW2, and the magnitude of the crosstalk between the first spatial channel and the second spatial channel is set to XT, mathematical formula (D) is used to calculate XT. a dB L≤a0+aθ+a2θ 2 …(C) a0=-3.40×10 -1 [dB], a1=-3.73×10 -2 [dB / degree], a2=7.46×10 0 [dB / degree 2 ] 5. The method for measuring spatial channel crosstalk according to claim 2, wherein: The space division multiplexing optical system is a space division multiplexing optical fiber, The light reflecting surface is the end face of the space division multiplexing optical fiber, When the wavelength of the test light is λ (μm), the circumference is π, the refractive index of the first spatial channel and the second spatial channel of the space-division multiplexing optical fiber is n, and the transmission loss coefficient of the first spatial channel and the second spatial channel is α (km -1 ), 0.5 times the mode field diameter of the first spatial channel and the second spatial channel is set to w (μm), the angle formed by the plane on the end face that touches the center of the first spatial channel and the second spatial channel and the plane that is orthogonal to the central axis of the spatial division multiplexing optical fiber is set to φ (rad), the length of the spatial division multiplexing optical fiber is set to L (km), the effective cross-sectional area of ​​the first spatial channel and the second spatial channel is set to A eff (μm 2 ), setting the Rayleigh scattering loss coefficient of the first spatial channel and the second spatial channel to α R (km -1 ), when the first optical power is set to PW10, the second optical power is set to PW20, and the magnitude of the crosstalk between the first spatial channel and the second spatial channel is set to XT, mathematical formula (E) is used to calculate XT, 6. The method for measuring spatial channel crosstalk according to claim 2, wherein: The space division multiplexing optical system is a space division multiplexing optical fiber, The light reflecting surface is the end face of the space division multiplexing optical fiber, When the wavelength of the test light is λ (μm), the circumference is π, the refractive index of the first spatial channel and the second spatial channel of the space-division multiplexing optical fiber is n, and the transmission loss coefficient of the first spatial channel and the second spatial channel is α (km -1 ), the length of the space division multiplexing optical fiber is set to L (km), the effective cross-sectional area of ​​the first spatial channel and the second spatial channel is set to A eff (μm 2 ), setting the Rayleigh scattering loss coefficient of the first spatial channel and the second spatial channel to α R (km -1 ), when the first optical power is set to PW10 and the second optical power is set to PW20, mathematical formula (F) is used to calculate XT, 7. The method for measuring spatial channel crosstalk according to claim 1, wherein: In the fourth step, The time-intensity waveform of the test light incident on the first spatial channel at the first input and output section and the light emitted from the first spatial channel at the first input and output section after being reflected in the first spatial channel, the second spatial channel, and the light reflecting surface is analyzed, and the power of the light reflected at a position corresponding to the length direction of the light reflecting surface and emitted from the first spatial channel is set as the first optical power. The time-intensity waveform of the test light incident on the first spatial channel at the first input and output section and the light emitted from the second spatial channel at the first input and output section after being reflected in the first spatial channel, the second spatial channel, and the light reflecting surface is analyzed, and the power of the light reflected at a position corresponding to the length direction of the light reflecting surface and emitted from the second spatial channel is set as the second optical power.

8. The method for measuring spatial channel crosstalk according to claim 1 or 7, wherein: The test light is pulsed light, The first optical power and the second optical power are the powers of light emitted from the first spatial channel and the second spatial channel, respectively, at a timing after a delay time equivalent to twice the distance between the first incident and output portion and the reflecting surface has passed after the test light is incident on the first spatial channel in the second step.

9. The method for measuring spatial channel crosstalk according to claim 7 or 8, wherein: The space division multiplexing optical system is a space division multiplexing optical fiber, The light reflecting surface is the end face of the space division multiplexing optical fiber, When the wavelength of the test light is λ (μm), the circumference of a circle is π, the refractive index of the first spatial channel and the second spatial channel of the space-division multiplexing optical fiber is n, 0.5 times the mode field diameter of the first spatial channel and the second spatial channel is w (μm), the angle formed by the plane on the end face that touches the center of the first spatial channel and the second spatial channel and the plane that is orthogonal to the central axis of the space-division multiplexing optical fiber is φ (rad), and the effective cross-sectional area of ​​the first spatial channel and the second spatial channel is A. eff (μm 2 ), setting the Rayleigh scattering loss coefficient of the first spatial channel and the second spatial channel to α R (km -1 ), when the pulse width of the test light propagating in the first spatial channel and the second spatial channel in the space-division multiplexing optical fiber is set to T (km), the value of mathematical formula (G) is greater than 10, 10. The method for measuring spatial channel crosstalk according to any one of claims 1 to 9, wherein: The space division multiplexing optical system is a space division multiplexing optical fiber or a space division multiplexing optical device. The light reflecting surface is the incident and exit surface of the space-division multiplexing optical fiber or the space-division multiplexing optical device. The first step includes forming the incident and exit surfaces by cutting or cleaving the incident and exit portions of the space-division multiplexing optical fiber or the space-division multiplexing optical device.

11. The method for measuring spatial channel crosstalk according to any one of claims 1 to 10, wherein: The light reflecting surface is the incident and exit surface of the space division multiplexing optical system. The first step includes providing a reflective film on the incident and exit surfaces or immersing the incident and exit surfaces in liquid metal.

12. The method for measuring spatial channel crosstalk according to any one of claims 1 to 11, wherein: The light reflecting surface is the incident and exit surface of the space division multiplexing optical system. The first step includes the step of disposing the incident and exit surfaces so as to be in contact with only gas.

13. The method for measuring spatial channel crosstalk according to claim 1, wherein: The first step includes the step of connecting the second incident and output surface of the second space-division multiplexing optical system to the incident and output surface of the space-division multiplexing optical system at the second incident and output portion, the second space-division multiplexing optical system is different from the space-division multiplexing optical system, and the first incident and output surface of the second space-division multiplexing optical system is provided with a reflective film serving as the light reflecting surface.

14. The method for measuring spatial channel crosstalk according to claim 1, wherein: The first step includes the step of optically coupling the second input and output surfaces of the first single-core optical fiber and the second single-core optical fiber with the first spatial channel and the second spatial channel at the second input and output portions, respectively, and the first input and output surfaces of the first single-core optical fiber and the second single-core optical fiber are provided with a reflective film serving as the light reflecting surface.

15. The method for measuring spatial channel crosstalk according to any one of claims 3 to 6, 9 and 10, wherein: The space division multiplexing optical fiber is a multi-core optical fiber or a multi-mode optical fiber.

16. The method for measuring spatial channel crosstalk according to claim 1 or 2, wherein: The space division multiplexing optical system is a multi-core optical device, a multi-core optical system, a multi-mode optical device or a multi-mode optical system.

17. The method for measuring spatial channel crosstalk according to any one of claims 1 to 16, wherein: The first spatial channel and the second spatial channel are a first fiber core and a second fiber core, respectively, or a first mode and a second mode, respectively.

18. A method for measuring inter-core crosstalk of a multi-core optical fiber, the method comprising: The first step is to form or set a light reflecting surface at the second end portion; In a second step, test light is made incident on the first fiber core at the first end portion; A third step is to reflect at least a portion of the test light on the light reflecting surface; In a fourth step, a first optical power and a second optical power are detected, wherein the first optical power is the power of the light in the at least a portion of the light that is emitted from the first fiber core at the first end, and the second optical power is the power of the light in the at least a portion of the light that is emitted from the second fiber core at the first end. as well as The fifth step is to calculate the magnitude of crosstalk between the first fiber core and the second fiber core based on the first optical power and the second optical power.

19. The method for measuring inter-core crosstalk of a multi-core optical fiber according to claim 18, wherein: The light reflecting surface is the end face of the multi-core optical fiber, The first step includes forming the end face by cleaving the multi-core optical fiber.

20. The method for measuring inter-core crosstalk of a multi-core optical fiber according to claim 18 or 19, wherein: The light reflecting surface is the end face of the multi-core optical fiber, The first step includes providing a reflective film on the end surface or immersing the end surface in liquid metal.

21. The method for measuring inter-core crosstalk of a multi-core optical fiber according to claim 18 or 19, wherein: The light reflecting surface is the end face of the multi-core optical fiber, The first step includes the step of disposing the end surface so as to be in contact with only gas.

22. The method for measuring inter-core crosstalk of a multi-core optical fiber according to any one of claims 18 to 21, wherein: The test light is pulsed light, The first optical power and the second optical power are the powers of light emitted from the first core and the second core, respectively, at a timing when a delay time equivalent to twice the distance between the first end and the reflecting surface has passed after the test light is incident on the first core in the second step.

23. The method for measuring inter-core crosstalk of a multi-core optical fiber according to claim 22, wherein: The light reflecting surface is the end face of the multi-core optical fiber, When the wavelength of the test light is λ (μm), the circumference is π, the refractive index of the core of the multi-core optical fiber is n, 0.5 times the mode field diameter of the first core and the second core is w (μm), the angle between the plane touching the center of the first core and the second core on the end face and the plane perpendicular to the central axis of the multi-core optical fiber is φ (rad), and the effective cross-sectional area of ​​the first core and the second core is A eff (μm 2 ), the Rayleigh scattering loss coefficient of the first fiber core and the second fiber core is set to α R (km -1 ), when the pulse width of the test light propagating in the core of the multi-core optical fiber is set to T (km), the value of the mathematical formula (H) is greater than 10, 24. The method for measuring inter-core crosstalk of a multi-core optical fiber according to claim 18, wherein: The first step includes connecting the second end face of a second multi-core optical fiber to the end face of the multi-core optical fiber at the second end portion, the second multi-core optical fiber being different from the multi-core optical fiber and having a first end face provided with a reflective film serving as the light reflecting surface.

25. The method for measuring inter-core crosstalk of a multi-core optical fiber according to claim 18, wherein: The first step includes the step of optically coupling the second end faces of the first single-core optical fiber and the second single-core optical fiber to the first fiber core and the second fiber core respectively at the second end portion, and the first end faces of the first single-core optical fiber and the second single-core optical fiber are provided with a reflective film serving as the light reflecting surface.

26. A device for measuring spatial crosstalk between channels of a space-division multiplexing optical system, wherein the space-division multiplexing optical system comprises a first input / output section and a second input / output section opposite to the first input / output section, and comprises N (N is an integer greater than or equal to 2) spatial channels, the device comprising: a light source unit configured to cause test light to be incident on the N spatial channels at the first incident and output portions; a light detecting unit configured to detect a first optical power and a second optical power, wherein the first optical power is the power of light emitted from a first spatial channel into which the test light is incident, in at least a portion of the test light reflected on a light reflecting surface formed or provided on the second incident and output unit; and the second optical power is the power of light emitted from a second spatial channel different from the first spatial channel, in the at least a portion of the light. A calculation unit calculates a magnitude of crosstalk between the first spatial channel and the second spatial channel based on the first optical power and the second optical power.

27. The spatial channel crosstalk measurement device according to claim 26, wherein: The spatial channel crosstalk measurement device further comprises: N three-port optical couplers, each having a first port, a second port, and a third port, and outputting light input to the first port from the second port and outputting light input to the second port from the third port; as well as an optical component, optically coupling the N spatial channels in the first input / output portion of the space-division multiplexing optical system to the second ports of the N three-port optical couplers, respectively; The light source unit is optically coupled to the first ports of the N three-port optical couplers. The light detection unit is optically coupled to the third ports of the N three-port optical couplers.

28. The spatial channel crosstalk measurement device according to claim 27, wherein: The light source unit has N light sources, The N light sources are optically coupled to the first ports of the N three-port optical couplers, respectively.

29. The spatial channel crosstalk measurement device according to claim 27, wherein: The light source unit has: Single light source; as well as A first optical switch selectively couples the single light source to the first port of any one of the N three-port optical couplers.

30. The spatial channel crosstalk measurement device according to any one of claims 27 to 29, wherein: The light detection unit has N light receivers. The N optical receivers are optically coupled to the third ports of the N three-port optical couplers, respectively.

31. The spatial channel crosstalk measurement device according to any one of claims 27 to 29, wherein: The light detection unit has: Single optical receiver; as well as The second optical switch selectively optically couples the single optical receiver to the third port of any one of the N three-port optical couplers.

32. The spatial channel crosstalk measurement device according to any one of claims 26 to 31, wherein: The time-intensity waveform of the test light incident on the first spatial channel at the first input / output portion and then emitted from the first spatial channel at the first input / output portion after being reflected within the first spatial channel, the second spatial channel, and the light reflecting surface is analyzed. The first optical power is the power of the light reflected at a position corresponding to the length direction of the light reflecting surface and emitted from the first spatial channel. The time-intensity waveform of the test light incident on the first spatial channel at the first input and output section and the light emitted from the second spatial channel in the first input and output section after being reflected in the first spatial channel, the second spatial channel, and the light reflecting surface is analyzed. The second optical power is the power of the light reflected at a position corresponding to the length direction of the light reflecting surface and emitted from the second spatial channel.

33. The spatial channel crosstalk measurement device according to any one of claims 26 to 31, wherein: The test light is pulsed light, The first optical power and the second optical power are powers of light emitted from the first spatial channel and the second spatial channel, respectively, at a timing when a delay time equivalent to twice the distance between the first incident and output portion and the reflecting surface has elapsed after the test light is incident on the first spatial channel.

34. The spatial channel crosstalk measurement device according to any one of claims 26 to 33, wherein: The light reflecting surface is the incident and exit surface of the space division multiplexing optical system. The spatial channel crosstalk measurement device further includes a holding unit that holds the space-division multiplexing optical system so that the incident and exit surfaces are in contact with only gas.

35. The spatial channel crosstalk measurement device according to any one of claims 26 to 33, wherein: The spatial channel crosstalk measurement device further includes a second space-division multiplexing optical system, wherein a first incident and output surface of the second space-division multiplexing optical system is provided with a reflective film serving as the light reflecting surface. The second incident and output surface of the second space-division multiplexing optical system is connected to the incident and output surface of the space-division multiplexing optical system at the second incident and output portion.

36. The spatial channel crosstalk measurement device according to any one of claims 26 to 33, wherein: The spatial channel crosstalk measurement device further includes N single spatial channel optical fibers, wherein a reflective film serving as the light reflecting surface is provided on a first incident and exit surface of the single spatial channel optical fibers. The second incident and output surfaces of the N single spatial channel optical fibers are optically coupled to the N spatial channels at the second incident and output portions.

37. The spatial channel crosstalk measurement device according to any one of claims 26 to 36, wherein: The space division multiplexing optical system is a space division multiplexing optical fiber.

38. The spatial channel crosstalk measurement device according to claim 37, wherein: The space division multiplexing optical fiber is a multi-core optical fiber or a multi-mode optical fiber.

39. The spatial channel crosstalk measurement device according to any one of claims 26 to 36, wherein: The space division multiplexing optical system is a multi-core optical device, a multi-core optical fiber, a multi-mode optical device, a multi-mode optical fiber, or an optical system formed by optically coupling two or more of these.

40. The spatial channel crosstalk measurement device according to any one of claims 26 to 36, wherein: The first spatial channel and the second spatial channel are a first fiber core and a second fiber core, respectively, or a first mode and a second mode, respectively.

41. A device for measuring inter-core crosstalk of a multi-core optical fiber, the device being a device for measuring inter-core crosstalk of the multi-core optical fiber, the multi-core optical fiber having a first end and a second end opposite to the first end, and having N cores, where N is an integer greater than or equal to 2, the device comprising: a light source unit configured to cause test light to be incident on each of the N fiber cores at the first end portion; a light detecting unit configured to detect a first optical power and a second optical power, wherein the first optical power is the power of light emitted from a first fiber core into which the test light is incident, of at least a portion of the test light reflected on a light reflecting surface formed or provided at the second end portion; and The calculation unit calculates the magnitude of crosstalk between the first core and the second core based on the first optical power and the second optical power.

42. The device for measuring inter-core crosstalk of a multi-core optical fiber according to claim 41, wherein: The inter-core crosstalk measuring device further comprises: N optical circulators, each having a first port, a second port, and a third port, and outputting light input to the first port from the second port and outputting light input to the second port from the third port; as well as an optical component for optically coupling the N fiber cores in the first end portion of the multi-core optical fiber to the second ports of the respective N optical circulators, The light source unit is optically coupled to the first ports of the N optical circulators. The light detection unit is optically coupled to the third ports of the N optical circulators.

43. The device for measuring inter-core crosstalk of a multi-core optical fiber according to claim 42, wherein: The light source unit has N light sources, The N light sources are optically coupled to the first ports of the N optical circulators, respectively.

44. The device for measuring inter-core crosstalk of a multi-core optical fiber according to claim 42, wherein: The light source unit has: Single light source; as well as A first optical switch selectively optically couples the single light source to the first port of any one of the N optical circulators.

45. The device for measuring inter-core crosstalk of a multi-core optical fiber according to any one of claims 42 to 44, wherein: The light detection unit has N light receivers. The N optical receivers are optically coupled to the third ports of the N optical circulators, respectively.

46. ​​The device for measuring inter-core crosstalk of a multi-core optical fiber according to claim 43 or 44, wherein: The light detection unit has: Single optical receiver; as well as The second optical switch selectively optically couples the single optical receiver to the third port of any one of the N optical circulators.

47. The device for measuring inter-core crosstalk of a multi-core optical fiber according to any one of claims 41 to 46, wherein: The test light is pulsed light, The first optical power and the second optical power are powers of light emitted from the first core and the second core, respectively, at a timing when a delay time equivalent to twice the distance between the first end and the reflecting surface has elapsed after the test light is incident on the first core.

48. The device for measuring inter-core crosstalk of a multi-core optical fiber according to any one of claims 41 to 47, wherein: The light reflecting surface is the end face of the multi-core optical fiber, The inter-core crosstalk measurement device further includes a holding portion that holds the multi-core optical fiber so that the end face is in contact with only gas.

49. The device for measuring inter-core crosstalk of a multi-core optical fiber according to any one of claims 41 to 47, wherein: The inter-core crosstalk measurement device further includes a second multi-core optical fiber, wherein a reflective film serving as the light reflecting surface is provided on a first end face of the second multi-core optical fiber. The second end face of the second multi-core optical fiber is connected to the end face of the multi-core optical fiber at the second end portion.

50. The device for measuring inter-core crosstalk of a multi-core optical fiber according to any one of claims 41 to 47, wherein: The inter-core crosstalk measuring device further includes N single-core optical fibers, wherein a reflective film serving as the light reflecting surface is provided on a first end face of the single-core optical fiber. The second end faces of the N single-core optical fibers are optically coupled to the N fiber cores at the second ends.

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