Optical fiber testing apparatus and optical fiber testing method

Abstract

To provide an optical fiber testing device and an optical fiber testing method capable of measuring distance dependency of inter-core crosstalk of a multi-core fiber.SOLUTION: The optical fiber test device 301 includes a measurer 10 that inputs an optical pulse to one core from one end A of the multi-core fiber 50 and measures a first light intensity of backscattered light output from the one core and a second light intensity of backscattered light output from another core at the one end A, and a calculator 20 that calculates an inter-core crosstalk between the one core and the another core from the first light intensity and the second light intensity.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to an optical fiber testing device and an optical fiber testing method for measuring crosstalk in an uncoupled multicore fiber. [Background technology]

[0002] Uncoupled multicore fibers are one of the promising optical fibers for realizing future high-capacity optical communications. Crosstalk between cores is an important parameter that limits the transmission capacity. Therefore, a method for evaluating the magnitude and longitudinal distribution of inter-core crosstalk in uncoupled multicore fibers is required to ensure the desired transmission capacity.

[0003] Non-Patent Document 1 and Non-Patent Document 2 disclose methods for measuring the longitudinal distribution of inter-core crosstalk when the signal transmission direction of each core in an uncoupled multi-core fiber is the same (unidirectional transmission). Non-Patent Document 3 proposes a method in which the signal transmission directions of adjacent cores are alternated (bidirectional transmission) in order to reduce the influence of inter-core crosstalk. Also disclosed is a method for measuring inter-core crosstalk when such bidirectional transmission is performed. [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] M. 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, pp. 12530-12540, 2012. [Non-patent document 2] M. Ohashi et al., “Simple backscattered power technique for measuring crosstalk of multi-core fibers,” in Proc. 17th Opto-Electronics and Communications Conference, P1_25, 2012. [Non-patent document 3] A. Sano et al., “Crosstalk-managed high capacity long haul multicore fiber transmission with propagation-direction interleaving,” J. Lightwave Technol., 32(16), 2771-2779, 2014. Summary of the Invention [Problem to be solved by the invention]

[0005] However, Non-Patent Document 1 and Non-Patent Document 2 do not disclose a method for measuring inter-core crosstalk when an uncoupled multi-core fiber is operated in bidirectional transmission. Furthermore, Non-Patent Document 3 discloses obtaining inter-core crosstalk during bidirectional transmission operation in the entire uncoupled multi-core fiber to be measured, but does not disclose a method for obtaining the longitudinal distribution (distance dependency) of inter-core crosstalk. In other words, there is currently a problem in that it is difficult to measure the distance dependence of inter-core crosstalk when bidirectional transmission is performed using an uncoupled multi-core fiber.

[0006] Therefore, in order to solve the above-mentioned problems, an object of the present invention is to provide an optical fiber testing device and an optical fiber testing method that can measure the distance dependency of inter-core crosstalk in an uncoupled multi-core fiber during bidirectional transmission. [Means for solving the problem]

[0007] In order to achieve the above object, the optical fiber testing device according to the present invention measures the light intensity of backscattered light generated by a test light pulse that is incident on a core from one end of an uncoupled multicore fiber, and calculates the distance dependency of inter-core crosstalk from the light intensity.

[0008] Specifically, the optical fiber testing device according to the present invention comprises: inputting an optical pulse into one core from one end of an uncoupled multicore fiber, and measuring a first optical intensity of backscattered light output from the one core at the one end; a measuring instrument that inputs an optical pulse from the one end of the uncoupled multicore fiber to one of two cores including the one core, and measures a second light intensity of backscattered light output from the other of the two cores at the one end; a computing unit that calculates, from the first light intensity and the second light intensity, inter-core crosstalk distance dependency between the two cores in a case where bidirectional transmission is performed between the two cores of the uncoupled multicore fiber in which light transmission directions are different from each other; Equipped with.

[0009] Further, the optical fiber testing method according to the present invention comprises: inputting an optical pulse into one core from one end of an uncoupled multicore fiber, and measuring a first optical intensity of backscattered light output from the one core at the one end; inputting an optical pulse from the one end of the uncoupled multicore fiber to one of two cores including the one core, and measuring a second light intensity of backscattered light output from the other of the two cores at the one end; and calculating, from the first light intensity and the second light intensity, inter-core crosstalk distance dependency between the two cores in a case where bidirectional transmission is performed between the two cores of the uncoupled multicore fiber in which light transmission directions are different from each other; Do the following.

[0010] The first method to calculate the distance dependency of inter-core crosstalk is calculating the optical intensity of the optical pulse that has passed through the one core of the uncoupled multicore fiber as a signal light intensity from the first light intensity; The product of the Rayleigh scattering coefficient, the backscattered light capture rate, and the integral value of the second light intensity integrated in the distance direction in the longitudinal direction of the uncoupled multicore fiber is defined as the leakage light intensity; and The ratio of the signal light intensity to the leakage light intensity is made dependent on the inter-core crosstalk distance. It is characterized by:

[0011] The second method for calculating the distance dependence of inter-core crosstalk is calculating crosstalk between the two cores from the first light intensity and the second light intensity when one-way transmission is performed in which the light transmission direction is the same between the two cores of the uncoupled multicore fiber; calculating a power coupling coefficient from the crosstalk; calculating a loss coefficient from the optical intensity of the optical pulse incident on the one core from the one end of the uncoupled multicore fiber and the first optical intensity; and calculating the inter-core crosstalk distance dependency by substituting the Rayleigh scattering coefficient, the backscattered light capture rate, and the loss coefficient into a power coupling equation of formula C1; It is characterized by:

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[0012] As described above, the present invention can provide an optical fiber testing device and an optical fiber testing method that can measure the distance dependency of inter-core crosstalk in an uncoupled multi-core fiber during bidirectional transmission. The above inventions can be combined as much as possible. [Effects of the Invention]

[0013] The present invention can provide an optical fiber testing device and an optical fiber testing method that can measure the distance dependency of inter-core crosstalk in an uncoupled multi-core fiber during bidirectional transmission. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a diagram illustrating an optical fiber testing device according to the present invention; [Figure 2] 1A to 1C are diagrams illustrating an optical fiber testing method according to the present invention. [Figure 3] 4A and 4B are diagrams illustrating waveforms of backscattered light obtained by the optical fiber testing device according to the present invention. [Figure 4] 10A and 10B are diagrams illustrating a method for calculating a loss value from the waveform of backscattered light obtained by the optical fiber testing device according to the present invention. [Figure 5] 10A and 10B are diagrams illustrating a method for calculating the cumulative value of backscattered light from the waveform of backscattered light obtained by the optical fiber testing device according to the present invention. [Figure 6] 1 is a diagram illustrating an embodiment of an optical fiber testing device according to the present invention; [Figure 7] 10A to 10C are diagrams illustrating the effects of the optical fiber testing device according to the present invention. [Figure 8] 10A and 10B are diagrams illustrating a method for obtaining the Rayleigh scattering coefficient and the capture rate. [Figure 9] 1 is a diagram illustrating the measurement principle of an optical fiber testing device according to the present invention. [Figure 10] 1 is a diagram illustrating the measurement principle of an optical fiber testing device according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0015] The following description of the preferred embodiments of the present invention will be given with reference to the accompanying drawings. The preferred embodiments described below are examples of the present invention, and the present invention is not limited to the preferred embodiments. In this specification and the drawings, components having the same reference numerals are intended to represent the same components.

[0016] FIG. 1 is a diagram illustrating an optical fiber testing apparatus 301 according to the present invention. The optical fiber testing apparatus 301 measures crosstalk during bidirectional transmission using an uncoupled multi-core fiber 50 as an optical fiber under test. The optical fiber testing apparatus 301 includes: Inputting an optical pulse from one end A of the uncoupled multi-core fiber 50 to one core (for example, #m), and measuring a first optical intensity of backscattered light output from the one core at the one end A (first measurement); and a measuring instrument 10 that inputs an optical pulse from one end A of the uncoupled multicore fiber 50 to one of two cores (e.g., #m or #n) including the one core, and measures (second measurement) a second light intensity of backscattered light output from the other of the two cores (core #n if the core to which the optical pulse is input is #m, or core #m if the core to which the optical pulse is input is #n); a calculator (20) that calculates, from the first light intensity and the second light intensity, the inter-core crosstalk distance dependency between the two cores in a case where bidirectional transmission is performed between the two cores of the uncoupled multi-core fiber (50) in which light transmission directions are different from each other; Equipped with. The above-mentioned "two cores" means adjacent cores in the case of a multi-core optical fiber having three or more cores.

[0017] FIG. 2 is a flowchart illustrating an optical fiber testing method performed by the optical fiber testing device 301. Inputting an optical pulse into one core from one end A of the uncoupled multi-core fiber 50, and measuring a first optical intensity of backscattered light output from the one core at the one end A (step S01); inputting an optical pulse from one end A of the uncoupled multi-core fiber 50 to one of the two cores including the one core, and measuring a second light intensity of backscattered light output from the other of the two cores at the one end A (step S02); calculating, from the first light intensity and the second light intensity, the inter-core crosstalk distance dependency between the two cores in the case where bidirectional transmission is performed between the two cores of the uncoupled multi-core fiber 50 in which the light transmission directions are different from each other; Do the following.

[0018] The measuring instrument 10 includes a test light generating unit 11 that generates an optical pulse, an input / output unit 12 that inputs the optical pulse to an uncoupled multicore fiber 50 and captures backscattered light from the uncoupled multicore fiber 50, and a receiving unit 13 that measures the intensity of the backscattered light. The measuring instrument 10 performs steps S01 and S02. The test light generating unit 11 and the input / output unit 12 perform processes m11, m12, m21, and m22, and the receiving unit 13 performs processes m13 and m23.

[0019] The input / output unit 12 includes, for example, an optical circulator 12 a, an optical switch 12 b, and an input / output device 12 c. The optical switch 12 b selects a core (#m or #n) of the uncoupled multi-core fiber 50 to which the optical pulse is incident, and selects a core (#m or #n) of the optical uncoupled multi-core fiber 50 from which the backscattering to be captured is emitted. The receiver 13 includes, for example, a photoelectric converter 13a that receives the backscattered light and converts it into an electrical signal, and an AD converter 13b that converts the electrical signal from analog to digital.

[0020] The calculator 20 performs step S03. The calculator 20 includes, for example, a waveform analyzer 20a that analyzes the waveform of the electrical signal converted into a digital signal, and a crosstalk calculator 20b that calculates crosstalk. The calculations performed by the calculator 20 will be explained in the following embodiment.

[0021] Example 1 This embodiment is a method for calculating the inter-core crosstalk of an uncoupled multi-core fiber during bidirectional transmission by utilizing the integration of backscattered light. Step S01: The measuring instrument 10 inputs an optical pulse from one end A of the uncoupled multi-core fiber 50 to a core #m, and measures the light intensity of backscattered light 1 from the core #m at the one end A. The backscattered light 1 is the intensity of backscattered light from the input core. Step S02: The measuring instrument 10 inputs an optical pulse from one end A of the uncoupled multi-core fiber 50 to core #n, and measures the light intensity of backscattered light 2 from core #m at the one end A. The backscattered light 2 is the intensity of backscattered light from an adjacent core. Note that if the loss coefficients of the cores of the uncoupled multi-core fiber 50 are considered to be equal, the backscattered light from core #n due to the optical pulse input to core #m may be taken as the backscattered light 2. Measuring instrument 10 can obtain the light intensity distribution shown in FIG. 3 by performing steps S01 and S02.

[0022] The calculator 20 The optical intensity of the optical pulse that has passed through the one core of the uncoupled multi-core fiber 50 is expressed as the signal optical intensity P signal and calculating from the first light intensity (backscattered light 1) as follows: The product of the Rayleigh scattering coefficient, the backscattered light capture efficiency, and the integral value obtained by integrating the second light intensity (backscattered light 2) over the longitudinal distance of the uncoupled multi-core fiber 50 is defined as the leakage light intensity P bs and Signal light intensity P signal and leakage light intensity P bs The ratio of the inter-core crosstalk distance dependency is set to It is characterized by:

[0023] Step S03: The calculator 20 performs the following calculation using the light intensity distribution in FIG. Step m31: The calculator 20 calculates the loss value of core #m over the entire length of the uncoupled multi-core fiber 50 from the backscattered light 1, as shown in Fig. 4. In an uncoupled multi-core fiber, the product of the power coupling coefficient and the fiber length is usually sufficiently smaller than 1, so the difference in intensity between the near end and the far end can be regarded as the loss value. Step m32: From the loss value of core #m calculated above, the signal light intensity P of the optical pulse output from core #m at the other end B is calculated. signalThe definition of inter-core crosstalk in uncoupled multicore fibers during bidirectional transmission is as described in Appendix 2. In this case, an optical pulse must be input to core #m at the other end B and the optical intensity of the optical pulse at core #m at one end A must be measured. However, whether the optical pulse is input to one end A and output from the other end B, or the optical pulse is input to the other end B and output from one end A (in the opposite direction), the signal optical intensity P signal Therefore, in this calculation, this idea is used to calculate the signal light intensity P signal Get. Step m33: Determine the Rayleigh scattering coefficient α of the uncoupled multi-core fiber 50 by any of the methods described in Appendix 1. s and the backscattered light capture rate B are obtained. Step m34: As shown in FIG. 5, the light intensity of the backscattered light 2 is integrated in the distance z direction to obtain the cumulative value (leakage light intensity) P bs Calculate.

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[0024] The calculator 20 calculates XT for each distance z. b By calculating the distance dependency of inter-core crosstalk in the case of bidirectional transmission,

[0025] Example 2 This embodiment is a method for calculating inter-core crosstalk during bidirectional transmission from inter-core crosstalk during unidirectional transmission in an uncoupled multi-core fiber. Step S01: The measuring instrument 10 inputs an optical pulse from one end A of the uncoupled multi-core fiber 50 to a core #m, and measures the light intensity of backscattered light 1 from the core #m at the one end A. The backscattered light 1 is the intensity of backscattered light from the input core. Step S02: The measuring instrument 10 inputs an optical pulse into the core #m from one end A of the uncoupled multi-core fiber 50, and measures the backscattered light 2 from the core #n at the one end A. The backscattered light 2 is the intensity of the backscattered light from the adjacent core. Measuring instrument 10 can obtain the light intensity distribution shown in FIG. 3 by performing steps S01 and S02.

[0026] The calculator 20 calculating crosstalk between the two cores when one-way transmission is performed in which the light transmission direction is the same between the two cores of the uncoupled multicore fiber 50 from the first light intensity (backscattered light 1) and the second light intensity (backscattered light 2); calculating a power coupling coefficient h from the crosstalk; calculating a loss coefficient α from the optical intensity of the optical pulse incident on one core (e.g., #m) from one end A of the uncoupled multi-core fiber 50 and the first optical intensity; and calculating the inter-core crosstalk distance dependency by substituting the Rayleigh scattering coefficient, the backscattered light capture rate, and the loss coefficient α into a power coupling equation of formula C1; It is characterized by:

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[0027] Step S03: The calculator 20 performs the following calculation using the light intensity distribution in FIG. Step m41: The crosstalk XT between two cores during one-way transmission can be calculated from the ratio of backscattered light 1 to backscattered light 2. The calculator 20 calculates the inter-core crosstalk XT during one-way transmission from the light intensity distribution in FIG. 3, and calculates the power coupling coefficient h according to the method described in Non-Patent Document 2. Step m42: The product of the Rayleigh scattering coefficient and the backscattered light capture efficiency of the uncoupled multi-core fiber 50 is obtained by any of the methods described in Appendix 1. Note that either step m41 or m42 may be performed first. Step m43: The inter-core crosstalk XT when bidirectional transmission is performed is calculated by substituting the various parameters obtained in steps m41 and m42 into equation (C1) that represents the inter-core crosstalk derived from the power coupling equation. b The method for deriving equation (C1) from the power combining equation is explained in Appendix 2.

[0028] The calculator 20 calculates XT for each distance z. b By calculating the distance dependency of inter-core crosstalk in the case of bidirectional transmission,

[0029] [Example] Optical fiber test equipment 301 for crosstalk XT b An experiment was conducted to confirm whether it is possible to measure the crosstalk XT of opposite transmissions using the methods of Example 1 and Example 2. b The crosstalk XT obtained by the power meter method is calculated. b The experimental system is as shown in Figure 6. The configuration in Figure 6(A) corresponds to the optical fiber testing device 301. Figure 6(B) shows the configuration using the power meter method. The uncoupled multi-core fiber 50 used was 4CF (SN:4CMCF2110-01) manufactured by Furukawa Electric Co., Ltd.

[0030] Figure 7 illustrates the experimental results. Figure 7(A) illustrates the OTDR waveform measured with the configuration of Figure 6(A). The wavelength of the optical pulse is 1550 nm, and the pulse width is 1 μs. The dashed line is the waveform of backscattered light 1 obtained from the core into which the optical pulse is incident. The solid line is the waveform of backscattered light 2 obtained from the core adjacent to the core into which the optical pulse is incident.

[0031] Figure 7(B) is a diagram explaining the distance dependency of crosstalk calculated from the OTDR waveform. The solid line is the result of the inter-core crosstalk distance dependency during one-way transmission. The dashed line is the result of the inter-core crosstalk distance dependency during two-way transmission calculated directly from the backscattered light intensity described in Example 1. The dotted line is the result of the inter-core crosstalk distance dependency during two-way transmission calculated from the fiber parameters described in Example 2. Both results were approximately the same value.

[0032] 7B, the circles indicate the crosstalk values ​​during bidirectional transmission obtained by the power meter method. b The crosstalk measured by the optical fiber testing equipment 301 during bidirectional transmission was found to be reliable.

[0033] [Appendix 1] How to obtain the Rayleigh scattering coefficient and capture rate (Method 1) When the mode field diameter of the core is known, the backscattered light capture efficiency B is calculated from the mode field diameter using equation (11).

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[0034] (Method 2) An optical fiber with a known Rayleigh scattering coefficient and capture rate is used as a reference fiber, and the Rayleigh scattering coefficient and capture rate of the optical fiber under test are obtained by the bidirectional OTDR method (see Document A). Figure 8(A) is a diagram explaining this method. A core 51a of a reference fiber 51, whose Rayleigh scattering coefficient and capture rate are known, is connected to one core (for example, #m) of an uncoupled multicore fiber 50. Test light is incident from both ends of this test system (the reference fiber 51 side and the other end B side) to measure the OTDR waveform. From this OTDR waveform, a waveform of the structural imperfection component I(z) as shown in Figure 8(B) can be obtained. The structural imperfection component I(z) can be expressed by the following equation. [Number 13] I(z)=10log[α s (z)B(z)]+a0 Here, a0 is a constant determined by the input power and loss. In the waveform of Figure 8(B), the section z s The structural imperfection component I(z) of the reference fiber 51 is a known value. t The structural imperfection component I(z) of the uncoupled multi-core fiber 50 can be obtained as a relative value of the structural imperfection component I(z) of the reference fiber 51. In other words, although the individual values ​​of the Rayleigh scattering coefficient and capture rate of the uncoupled multi-core fiber 50 are unknown, the Rayleigh scattering coefficient α s and the capture rate B can be calculated from the structural imperfection I(z) of the reference fiber 51. (Reference A) Kazuhide Nakajima et al., “Chromatic Dispersion Distribution Measurement Along a Single-Mode Optical Fiber”, JOURNAL OF LIGHTWAVE TECHNOLOGY, VOL. 15, NO. 7, JULY 1997

[0035] [Appendix 2] Crosstalk evaluation technique for uncoupled multi-core fibers (1) Definition of crosstalk Generally, crosstalk is defined as the optical power P signal and the optical power P of the signal to be blocked. noise As mentioned above, crosstalk XT in one-way transmission is the power ratio of the signal light incident on core #m at one end A to the signal light output from core #m at the other end B, and the leakage light output from the adjacent core #n (XT=P noise / P signal ) (Fig. 9(A)). On the other hand, crosstalk XT b When the leakage light from the non-adjacent core is sufficiently small, the signal light P signal and the other signal light incident from adjacent core #n at one end A is returned from core #m at one end A. bs Power ratio (XT b =P bs / P signal ) (Figure 9(B)). (2) Relationship between crosstalk and fiber parameters Here, we formulate the relationship between crosstalk and fiber parameters in a two-core fiber (cores #m and #n). The fiber loss in each core is equal, and various parameters (fiber loss α, power coupling coefficient h, backscattered light capture rate B, Rayleigh scattering coefficient α) are used. s ) is assumed to be uniform along the length of the optical fiber. The fiber length is L (m). There is no Fresnel reflection. Under this assumption, the following relationship holds between adjacent cores even in a multi-core fiber with three or more cores. i) In the case of one-way transmission The optical intensity of each core at position z in a two-core fiber can be described by the following power combining equation:

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[0036] 10: Measuring instrument 11: Test light generation unit 12: Input / output section 12a: Optical circulator 12b: Optical switch 12c: Input / output devices 13: Receiving unit 13a: Photoelectric conversion unit 13b: AD converter 20: Arithmetic unit 20a: Waveform analysis section 20b: Crosstalk calculation section 50: Optical fiber under test (uncoupled multi-core fiber) 51: Reference fiber 301: Optical fiber testing equipment

Claims

1. An optical fiber testing device for testing a multi-core fiber, a pulse light source that inputs an optical pulse from one end of the multicore fiber to one core; a receiving unit at one end of the multicore fiber that measures a first light intensity of backscattered light output from the one core generated by the optical pulse input to the one core and a second light intensity of backscattered light output from the other core; a calculator that calculates inter-core crosstalk between the one core and the other core of the multicore fiber from the first light intensity and the second light intensity; It is equipped with The computing unit calculating the optical intensity of the optical pulse that has passed through the one core of the multicore fiber as a signal light intensity from the first light intensity; calculating a leakage light intensity from an integral value obtained by integrating the second light intensity over a distance in the longitudinal direction of the multi-core fiber; and The ratio of the signal light intensity to the leakage light intensity is set as the inter-core crosstalk. An optical fiber testing device comprising:

2. An optical fiber testing method for testing a multi-core fiber, comprising: inputting an optical pulse into one core from one end of the multicore fiber; measuring, at one end of the multicore fiber, a first light intensity of backscattered light output from the one core generated by the optical pulse input to the one core and a second light intensity of backscattered light output from the other core; and calculating inter-core crosstalk between the one core and the other core of the multicore fiber from the first light intensity and the second light intensity; We are doing In the calculation of the inter-core crosstalk, calculating the optical intensity of the optical pulse that has passed through the one core of the multicore fiber as a signal light intensity from the first light intensity; calculating a leakage light intensity from an integral value of the second light intensity integrated in a distance direction in the longitudinal direction of the multi-core fiber; and The ratio of the signal light intensity to the leakage light intensity is set as the inter-core crosstalk. An optical fiber testing method comprising:

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