Optical fiber testing device and optical fiber testing method

Abstract

The purpose of the present invention is to provide an optical fiber test device and an optical fiber test method that make it possible to obtain both unidirectional crosstalk and bidirectional crosstalk in a non-coupled multicore fiber in a short period of time and with reduced man-hours.　An optical fiber test device 301 according to the present invention comprises: a light input unit 10 that inputs test light to any one of cores at one end A of a non-coupled multicore fiber 50; a light receiving unit 20 that receives output light outputted from each core at an opposite end B of the non-coupled multicore fiber 50 due to the test light, and that measures the optical intensity of the output light from each core; and a computation unit 30 that calculates, from the optical intensity of the output light, unidirectional transmission crosstalk when performing unidirectional transmission in which the light transmission direction is the same between two cores of the non-coupled multicore fiber 50, and that calculates, from the unidirectional transmission crosstalk, bidirectional transmission crosstalk when performing bidirectional transmission in which the light transmission direction is different between the two cores of the non-coupled multicore fiber 50.

Description

[Technical field]

[0001] The present disclosure relates to an optical fiber testing apparatus 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 large-capacity optical communications in the future. The crosstalk between the cores of an uncoupled multicore fiber is an important parameter that limits the transmission capacity. Therefore, a method for evaluating the crosstalk between the cores of an uncoupled multicore fiber is required to ensure the desired transmission capacity.

[0003] Here, since crosstalk when the signal propagation directions of adjacent cores in an uncoupled multicore fiber are the same (one-way crosstalk) and inter-core crosstalk when the signal propagation directions are alternated (bidirectional crosstalk) are significantly different, it is important to understand the characteristics of each. Non-Patent Documents 1 and 2 disclose a method for measuring one-way crosstalk. Non-Patent Document 3 discloses a method for measuring bidirectional crosstalk. [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] K. Takenaga et al., “An investigation on crosstalk in multi-core fibers by introducing random fluctuation along longitudinal direction,” IEICE Trans. Commun., vol. E94-B, no. 2, pp. 409-416, 2011. [Non-Patent Document 2] T. Hayashi et al., “Characterization of crosstalk in ultra-low-crosstalk multi-core fiber,” J. Lightw. Technol., vol. 30, no. 4, pp. 583-589, 2012. [Non-Patent Document 3] T. Ito et al., “Reduction of influence of inter-core cross-talk in MCF with bidirectional assignment between neighboring cores,” Proc. OFC 2013, paper OTh3K.2. Summary of the Invention [Problem to be solved by the invention]

[0005] Here, the measurement of one-way crosstalk (the methods described in Non-Patent Documents 1 and 2) and the measurement of bidirectional crosstalk (the method described in Non-Patent Document 3) are different in measurement method and device configuration. In other words, in order to grasp both the one-way crosstalk and the bidirectional crosstalk of an uncoupled multicore fiber, different measurements need to be performed, which poses a problem that it is difficult to shorten the measurement time and reduce the number of steps.

[0006] Therefore, in order to solve the above-mentioned problems, the present invention aims to provide an optical fiber testing device and an optical fiber testing method that can obtain both the one-way crosstalk and the bidirectional crosstalk of an uncoupled multicore fiber in a short time and with few labor hours. [Means for solving the problem]

[0007] In order to achieve the above object, an optical fiber testing device according to the present invention measures only the one-way crosstalk of an uncoupled multi-core fiber, and calculates the bi-directional crosstalk from the measurement result.

[0008] Specifically, the optical fiber testing device according to the present invention comprises: an optical input unit for inputting a test light to any one of the cores at one end of an uncoupled multicore fiber; a light receiving unit that receives output light output from each core at the other end of the uncoupled multi-core fiber in response to the test light and measures the light intensity of the output light from each core; a calculation unit that calculates, from the light intensity of the output light, one-way transmission crosstalk when one-way transmission is performed between the two cores of the uncoupled multi-core fiber in which the light transmission direction is the same, and calculates, from the one-way transmission crosstalk, a bidirectional transmission crosstalk when bidirectional transmission is performed between the two cores of the uncoupled multi-core fiber in which the light transmission directions are different from each other; Equipped with.

[0009] Further, the optical fiber testing method according to the present invention comprises: inputting test light into any one of the cores at one end of an uncoupled multicore fiber; receiving output light output from each core at the other end of the uncoupled multi-core fiber in response to the test light, and measuring the optical intensity of the output light from each core; calculating, from the optical intensity of the output light, a one-way transmission crosstalk when one-way transmission is performed in which the optical transmission direction is the same between the two cores of the uncoupled multi-core fiber; and Calculating bidirectional transmission crosstalk from the one-way transmission crosstalk when bidirectional transmission is performed between the two cores of the uncoupled multicore fiber in which the light transmission directions are different from each other. Do the following.

[0010] Since the measurement of the bidirectional crosstalk can be omitted, both the one-way crosstalk and the bidirectional crosstalk of the uncoupled multicore fiber can be obtained in a short time with few man-hours. Therefore, the present invention can provide an optical fiber testing device and an optical fiber testing method that can obtain both the one-way crosstalk and the bidirectional crosstalk of the uncoupled multicore fiber in a short time with few man-hours.

[0011] The bidirectional crosstalk is calculated as follows. Calculating the one-way transmission crosstalk from the optical intensity of the output light of the one core and the optical intensity of the output light of the other core; calculating a power combining coefficient from the one-way transmission crosstalk; and Calculating the bidirectional transmission crosstalk by substituting the Rayleigh scattering coefficient, the backscatter capture rate, and the loss coefficient into a power combining equation of number C1.

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[0012] The above-mentioned inventions can be combined as much as possible. Effect of the Invention

[0013] The present invention can provide an optical fiber testing apparatus and an optical fiber testing method that can obtain both the one-way crosstalk and the bidirectional crosstalk of an uncoupled multi-core fiber in a short time with few steps. [Brief description of the drawings]

[0014] [Figure 1] 1 is a diagram illustrating an optical fiber testing device according to the present invention; [Diagram 2] 1A to 1C are diagrams illustrating an optical fiber testing method according to the present invention. [Diagram 3] FIG. 1 is a diagram for explaining the definition of crosstalk. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] The embodiments of the present invention will be described with reference to the accompanying drawings. The embodiments described below are examples of the present invention, and the present invention is not limited to the following embodiments. Note that components with the same reference numerals in this specification and drawings indicate 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 both one-way crosstalk and two-way crosstalk of an uncoupled multi-core fiber 50, which is an optical fiber under test. The optical fiber testing apparatus 301 includes: an optical input unit 10 for inputting test light to any one of the cores at one end A of an uncoupled multi-core fiber 50; a light receiving unit that receives output light output from each core at the other end B of the uncoupled multi-core fiber by the test light and measures the light intensity of the output light from each core; a calculation unit (30) that calculates, from the light intensity of the output light, one-way transmission crosstalk in the case where one-way transmission is performed between the two cores of the uncoupled multi-core fiber (50) in the same light transmission direction, and calculates, from the one-way transmission crosstalk, a bidirectional transmission crosstalk in the case where bidirectional transmission is performed between the two cores of the uncoupled multi-core fiber (50) in the different light transmission directions; Equipped with.

[0017] The light input unit 10 has a test light generating unit 11 that generates test light, and a test light input unit 12 that inputs test light from one end A of the uncoupled multi-core fiber 50 to an arbitrary core. The light receiving unit 20 has a test light output unit 21 that selectively outputs light output from an arbitrary core at the other end B of the uncoupled multi-core fiber 50 to the light receiving unit 22, and a photoelectric converter 22 that photoelectrically converts the test light output from the test light output unit 21. The calculation unit 30 calculates crosstalk from the signal output from the photoelectric converter 22.

[0018] The test light generating unit 11 is composed of, for example, a broadband light source and a wavelength filter. A single wavelength light source or a wavelength-variable light source may also be used. The test light input section 12 is, for example, a fan-in fan-out device, and may be realized by adjusting the optical axis between a core of a single optical fiber and any core of the uncoupled multi-core fiber 50. The test light output unit 21 is, for example, a fan-in fan-out device, and may be realized by adjusting the optical axis between a core of a single optical fiber and any core of the uncoupled multi-core fiber 50. The photoelectric converter 22 is, for example, a photodetector. A plurality of photodetectors may be used to simultaneously perform photoelectric conversion on the test light output from a plurality of cores.

[0019] FIG. 2 is a flow chart illustrating an optical fiber testing method performed by the optical fiber testing device 301. The method includes the steps of: Inputting test light into any one of the cores at one end A of the uncoupled multi-core fiber 50 (step S1); receiving output light output from each core at the other end B of the uncoupled multi-core fiber 50 by the test light, and measuring the light intensity of the output light from each core (step S2); Calculating, from the optical intensity of the output light, one-way transmission crosstalk in the case where one-way transmission is performed in which the optical transmission direction is the same between the two cores of the uncoupled multi-core fiber 50 (step S3); and Calculating, from the one-way transmission crosstalk, the bidirectional transmission crosstalk when bidirectional transmission is performed between the two cores of the uncoupled multicore fiber 50 in which the light transmission directions are different from each other (step S4). Do the following.

[0020] The light input unit 10 generates test light having a desired wavelength, and inputs the test light to an arbitrary core at one end A of the uncoupled multi-core fiber 50 in step S1. The light receiving unit 20 measures the light intensity of the light output from the core to which the test light is input and the other cores at the other end B of the uncoupled multi-core fiber 50. The light intensities output from the multiple cores may be measured sequentially or simultaneously. The calculation unit 30 performs step S3 of calculating one-way crosstalk from the light intensity of the light output from each core obtained in step S2, and step S4 of calculating bidirectional crosstalk from the value of the one-way crosstalk.

[0021] The calculation contents performed by the calculation unit 30 will now be described in detail. In step S3, the one-way crosstalk is calculated as follows. At the other end B of the uncoupled multi-core fiber 50, the optical intensity of the test light output from the core i to which the test light is input is expressed as P i , the optical intensity of the light output from the other core j is P j One-way crosstalk XT f [dB] is calculated using the following formula:

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[0022] In step 4, the bidirectional crosstalk is calculated as follows: Step m1: One-way crosstalk XT f from the power coupling coefficient h[m -1 ] is calculated (see reference 1).

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[0023] Step m2: The Rayleigh scattering coefficient α of the uncoupled multi-core fiber 50 is calculated by the method described in Appendix 1. s and the backscattered light capture rate B is obtained. Step m3: The various parameters obtained in steps m1 and m2 are calculated as the bidirectional crosstalk XT using the equation (C1) derived from the power coupling equation.b The method for deriving formula (C1) from the power combining equation is explained in Appendix 2.

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[0024] [Appendix 1] How to obtain the Rayleigh scattering coefficient and capture rate The loss coefficient α and mode field diameter w [m] of the uncoupled multi-core fiber 50 are items obtained during manufacturing and are known values. From these values, the capture efficiency B and the Rayleigh scattering coefficient α s Calculate. The capture rate B is calculated from the mode field diameter w using the following formula:

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[0025] [Appendix 2] Crosstalk evaluation technology for uncoupled multicore 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 Crosstalk in one-way transmission XT f is the ratio of the signal light input from core i at one end A to the signal light output from core i at the other end B and the leakage light output from the adjacent core j (XTf =P noise / P signal ) (Figure 3(A)). On the other hand, crosstalk in bidirectional transmission is b When the leakage light from non-adjacent cores is sufficiently small, the signal light P signal Another signal light input from adjacent core j at one end A is returned from core i at one end A as P bs Ratio of (XT b =P bs / P signal ) (Figure 3(B)). (2) Relationship between crosstalk and fiber parameters Here, we formulate the relationship between crosstalk and fiber parameters in a two-core fiber. 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 s ) is assumed to be uniform along the longitudinal direction of the optical fiber. The fiber length is L (m). There is no Fresnel reflection. Under these assumptions, the following relationship holds between adjacent cores even in a multicore fiber with three or more cores. i) In case of one-way transmission The optical intensity of each core at position z in a two-core fiber can be described by the power combination equation:

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[0026] 10: Optical input section 11: Test light generation unit 12: Test light input section 20: Light receiving part 21: Test light output section 22: Photoelectric converter 30: Arithmetic section 301: Optical fiber testing equipment

Claims

1. an optical input unit for inputting a test light to any one of the cores at one end of the uncoupled multicore fiber; a light receiving unit that receives output light output from each core at the other end of the uncoupled multi-core fiber in response to the test light and measures the light intensity of the output light from each core; a calculation unit that calculates, from the light intensity of the output light, one-way transmission crosstalk when one-way transmission is performed between the two cores of the uncoupled multi-core fiber in which the light transmission direction is the same, and calculates, from the one-way transmission crosstalk, a bidirectional transmission crosstalk when bidirectional transmission is performed between the two cores of the uncoupled multi-core fiber in which the light transmission directions are different from each other; An optical fiber testing device comprising:

2. The calculation unit is calculating the one-way transmission crosstalk from the optical intensity of the output light of the one core and the optical intensity of the output light of the other core; calculating a power combining coefficient from the one-way transmission crosstalk; and Calculating the bidirectional transmission crosstalk by substituting a Rayleigh scattering coefficient, a backscattered light capture rate, and a loss coefficient into a power combining equation of formula C1; 2. The optical fiber testing device according to claim 1, [Number C1] where α is the loss coefficient, α ｓ is the Rayleigh scattering coefficient, B is the backscattered light capture rate, h is the power coupling coefficient, and L is the fiber length of the uncoupled multicore fiber.

3. inputting test light into any one of the cores at one end of an uncoupled multicore fiber; receiving output light output from each core at the other end of the uncoupled multi-core fiber by the test light, and measuring the optical intensity of the output light from each core; calculating, from the light intensity of the output light, one-way transmission crosstalk in a case where one-way transmission is performed in which the light transmission direction is the same between the two cores of the uncoupled multi-core fiber; and Calculating bidirectional transmission crosstalk from the one-way transmission crosstalk when bidirectional transmission is performed between the two cores of the uncoupled multicore fiber in which the light transmission directions are different from each other. Optical fiber testing method.

4. calculating the one-way transmission crosstalk from the optical intensity of the output light of the one core and the optical intensity of the output light of the other core; calculating a power combining coefficient from the one-way transmission crosstalk; and Calculating the bidirectional transmission crosstalk by substituting a Rayleigh scattering coefficient, a backscattered light capture rate, and a loss coefficient into a power combining equation of formula C1; 4. The optical fiber testing method according to claim 3, further comprising: [Number C1] where α is the loss coefficient, α ｓ is the Rayleigh scattering coefficient, B is the backscattered light capture rate, h is the power coupling coefficient, and L is the fiber length of the uncoupled multicore fiber.

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