Characteristic measurement apparatus, system, and method

Abstract

This disclosure aims to provide a technique for efficiently measuring the statistical characteristics of power coupling coefficients. [Solution] The characteristic measuring device 40 of the present disclosure calculates a power coupling coefficient corresponding to each backscattered light measured by a measuring device 20 that repeatedly measures backscattered light from at least one core of a coupled multicore fiber while changing the wavelength of the wavelength-swept light.

Description

Technical Field

[0001] The present disclosure relates to a technique for measuring statistical characteristics of the power coupling coefficient of a coupled multi-core fiber.

Background Art

[0002] In recent years, research and development of spatial division multiplexing transmission technology has been carried out as a means to increase the transmission capacity per optical fiber. In particular, a coupled multi-core fiber (MCF) has attracted attention as a promising transmission medium because of its excellent optical characteristics such as low spatial mode dispersion and low mode-dependent loss. Since these optical characteristics of the coupled MCF depend on the power coupling coefficient, which is the strength of light coupling between cores, it is important to grasp the power coupling coefficient.

[0003] Here, since the power coupling coefficient of the coupled MCF changes due to bending and twisting applied to the fiber, it is necessary to grasp statistical characteristics such as the average value and variance. Therefore, in Non-Patent Document 1, statistical characteristics of the power coupling coefficient are obtained by repeatedly measuring while rewinding the fiber. Specifically, in Non-Patent Document 1, an optical frequency domain reflectometer (OFDR) is used. Wavelength-swept light is incident from one core of the MCF, the backward scattered light from each core is measured, and the power coupling coefficient is calculated from the ratio of the backward scattered light intensities between the cores.

[0004] Then, in Non-Patent Document 1, statistical characteristics of the power coupling coefficient are obtained by repeatedly measuring while rewinding the fiber for each measurement. However, with this method, it is necessary to rewind the fiber for each measurement, resulting in an extremely long measurement time.

Prior Art Documents

Non-Patent Documents

[0005]

Non-Patent Document 1

[0006] Therefore, this disclosure aims to provide a technique for efficiently measuring the statistical characteristics of power coupling coefficients. [Means for solving the problem]

[0007] To achieve the above objectives, the characteristic measurement apparatus, system, and method of this disclosure employ a method in which a measuring device repeatedly measures backscattered light from each core and calculates the power coupling coefficient corresponding to each measured backscattered light.

[0008] Specifically, the characteristic measuring device disclosed herein is: A measurement device repeatedly measures the backscattered light from each core of a coupled multicore fiber while varying the wavelength of the wavelength-swept light, and calculates the corresponding power coupling coefficient for each backscattered light measured by the device.

[0009] In the above configuration, the statistical characteristics of the power coupling coefficients may be calculated from the multiple power coupling coefficients that have been calculated.

[0010] Alternatively, the power coupling coefficient may be calculated at a position where the difference in backscattered light intensity between cores is below a predetermined threshold.

[0011] Furthermore, specifically, the characteristic measurement system disclosed herein is: The above characteristic measuring device and, A measurement device that repeatedly measures backscattered light from each core while varying the wavelength of the wavelength-swept light, and injecting it into at least one core of a coupled multicore fiber. It is equipped with.

[0012] In the above configuration, the measuring device may perform measurements such that the wavelength sweep range of the wavelength sweep light does not overlap before and after changing the wavelength of the wavelength sweep light.

[0013] Specifically, the characteristic measurement method of the present disclosure incides at least one of the cores of the coupled multi-core fiber while changing the wavelength of the wavelength-scanned light, repeatedly measures the backscattered light from each core, and calculates the corresponding power coupling coefficient for each measured backscattered light.

[0014] In the above configuration, statistical characteristics of the power coupling coefficient may be calculated from the calculated plurality of power coupling coefficients.

[0015] The characteristic measurement device of the present invention can also be realized by a computer and a program, and it is also possible to record the program on a recording medium or provide it through a network. The program of the present disclosure is a program for causing a computer to realize each function provided in the device according to the present disclosure, and is a program for causing a computer to execute each procedure provided in the method executed by the device according to the present disclosure.

[0016] In addition, the above disclosures can be combined as much as possible.

Advantages of the Invention

[0017] According to the present disclosure, statistical characteristics of the power coupling coefficient can be efficiently measured.

Brief Description of the Drawings

[0018] [Figure 1] It is a diagram for explaining the configuration of the characteristic measurement system according to an embodiment of the present disclosure. [Figure 2] It is a flowchart for explaining the processing flow of the characteristic measurement system. [Figure 3] It is a diagram for explaining the relationship between the wavelength sweep range and the sweep interval. [Figure 4] It is a diagram for explaining the case where the sweep ranges overlap. [Figure 5] It is a diagram for explaining the measurement system of the backscattered light intensity from the incident core #1. [Figure 6]This diagram illustrates the measurement system for backscattered light intensity from adjacent core #2. [Figure 7] This graph shows an example of an actual waveform measurement in a 2-core fiber. [Figure 8] This is a histogram of the power coupling coefficients measured in practice. [Modes for carrying out the invention]

[0019] Embodiments of this disclosure will be described in detail below with reference to the drawings. However, this disclosure is not limited to the embodiments shown below. These examples are illustrative, and this disclosure can be implemented in various modified and improved forms based on the knowledge of those skilled in the art. In this specification and in the drawings, components with the same reference numerals refer to the same components.

[0020] The characteristic measurement system 100 according to the embodiment of this disclosure will be described with reference to Figures 1 to 8.

[0021] [Overall structure] As shown in Figure 1, the characteristic measurement system 100 comprises a measuring device 20, an optical multiplexer / demultiplexer 30, and a characteristic measurement device 40. In this embodiment, a device configuration for measuring the power coupling coefficient is shown using a 2-core (core #1, core #2) fiber as an example. However, this disclosure is not limited to 2-core fibers, and the power coupling coefficient of multi-core fibers with more cores can be measured.

[0022] The measuring device 20 measures the spectrum of backscattered light reflected or scattered by the optical fiber 1 under test, based on the principle of OFDR (Optical Frequency Domain Reflectometry). The measuring device 20 comprises a wavelength-swept light source 21, couplers 22 and 24, a circulator 23, and a light receiver 25.

[0023] The wavelength-swept light source 21 emits light at a predetermined sweep interval. The coupler 22 splits the light from the wavelength-swept light source 2 into reference light and probe light. The probe light split by the coupler 22 is incident on the optical fiber 1 under test via the circulator 23. The coupler 24 combines the signal light, which is the backscattered light in the optical fiber 1 under test, with the reference light split by the coupler 22. The photodetector 25 receives the interference light combined by the coupler 24. This allows the longitudinal backscattered light intensity of the optical fiber 1 under test to be obtained. Note that the object under test is not limited to an optical fiber, but may be other optical devices.

[0024] The optical multiplexer / demultiplexer 30 is configured to combine and demultiplex light between the cores of the optical fiber 1 under test. In this embodiment, the incident light on a predetermined core (e.g., core #1) of the optical fiber 1 under test is combined, and the backscattered light from the optical fiber 1 under test is demultiplexed for each core. More detailed measurements using the optical multiplexer / demultiplexer 30 will be described later.

[0025] The characteristic measurement device 40 comprises a control unit 41 and a calculation unit 42. The control unit 41 controls the wavelength-swept light source 21 based on the settings of the wavelength-swept range and the sweep interval. Specifically, in this embodiment, the backscattered light is measured repeatedly while changing the wavelength of the wavelength-swept light source 21. The settings of the wavelength-swept range and the sweep interval may be stored in the memory area of ​​the control unit 41.

[0026] The calculation unit 42 repeatedly calculates the power coupling coefficient for each measurement of the measuring device 20 based on the output signal corresponding to the backscattered light intensity from the photodetector 25. The calculation unit 42 also calculates the average value and variance of the calculated power coupling coefficient.

[0027] Specifically, the characteristic measuring device 40 or characteristic measuring method is The measurement device 20 repeatedly measures the backscattered light from at least one core of a coupled multicore fiber while varying the wavelength of the wavelength-swept light, and calculates the power coupling coefficient corresponding to each backscattered light measured by the device.

[0028] Furthermore, the characteristic measurement device 40 or characteristic measurement method is The statistical characteristics of the power coupling coefficients are calculated from the multiple power coupling coefficients that have been calculated.

[0029] The characteristic measurement device 40 can also be implemented using a computer and a program, and the program can be recorded on a recording medium or provided via a network. The control unit 41 may control the wavelength-swept light source 21 based on the calculation result of the power coupling coefficient by the calculation unit 42. Furthermore, the measuring device 20, the photomultiplexer / demultiplexer 30, and the characteristic measurement device 40 may be configured as separate devices or as a single device.

[0030] [Measurement principle] Here, we will explain why the measurement results of this embodiment are equivalent to the measurement results of Non-Patent Document 1.

[0031] First, let's consider the exchange of light between the mth and nth cores when a multicore fiber, which has multiple cores, is wound with a constant bending radius. The phase of each core can be expressed by the following equation.

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[0032] Light is exchanged between cores when the propagation constants are matched. In other words, it is not when the phases of each core become equal.

[0033] In the above equation, the propagation constants of each core coincide when cosθ(z')=0. That is, light is exchanged between the cores when the condition θ=(π / 2)×a is satisfied, where a is an integer.

[0034] Assuming θ = γz, equations (1-1) and (1-2) can be expressed as follows.

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[0035] Therefore, the phase difference of light between cores can be expressed by the following equation.

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[0036] To obtain the statistical characteristics of the power coupling coefficient, the inter-core phase difference in equation (3) needs to change randomly. The condition for matching the propagation constants between cores is θ = γz = (π / 2) × a, so the inter-core phase difference at the position where the propagation constants match can be expressed by the following equation.

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[0037] From equation (4), it can be seen that the inter-core phase difference at the position where the propagation constants match depends on the torsion ratio and wavelength. In other words, the inter-core phase difference changes at the position where each propagation constant in the longitudinal direction of the fiber matches as the wavelength changes. Physically rewinding the fiber is equivalent to changing the torsion ratio γ in equation (4). On the other hand, changing the wavelength as described in this disclosure is equivalent to changing the wavelength λ in equation (4). Since both of the above operations produce the same effect physically, changing the wavelength can reflect the change in the coupling constant in the same way as when the fiber is rewound.

[0038] For simplicity, the above explanation used the conditions that R is constant and θ = γz, so the inter-core phase difference at the position where the propagation constants match could be expressed as in equation (4). However, in actual multi-core fibers, R is not constant along the longitudinal direction, and the torsion ratio γ is also not constant. Even in this case, the inter-core phase difference changes at the position where each propagation constant in the longitudinal direction of the fiber matches due to the change in wavelength. Therefore, the value of the power coupling coefficient, which is a concept similar to crosstalk, also takes statistically varied values.

[0039] [Processing flow] The processing flow of the characteristic measurement system 100 will be explained with reference to Figures 2 to 7. Figure 2 is a flowchart illustrating the processing flow of the characteristic measurement system 100.

[0040] In step S1, the control unit 41 sets the wavelength sweep range and sweep interval of the wavelength sweep light source 21. Based on these settings, the control unit 41 controls the wavelength sweep light source 21.

[0041] In step S2, the wavelength-swept light source 21 emits light whose wavelength is changed by the sweep interval based on control from the control unit 41. Note that the measurement may be performed without sweeping the wavelength during the initial measurement. Also, the sweep interval may be the same for all cores.

[0042] Here, the settings for the wavelength sweep range and wavelength interval will be explained with reference to Figures 3 and 4. Each figure shows an image of the wavelength sweep range and sweep interval. As shown in the upper part of Figure 3, in this embodiment, measurements are repeated across the entire wavelength sweep range while shifting the wavelength of the swept light by a predetermined sweep interval. Here, as shown in the lower part of Figure 3, the sweep range of the swept light may be set so that it does not overlap before and after the wavelength change.

[0043] Based on Figure 4, we will explain why the sweep range of wavelength-swept light should not overlap before and after the wavelength change. Figure 4 shows a case where the sweep ranges overlap. That is, the sweep interval is narrow, and the sweep ranges of adjacent wavelength-swept light overlap. When measuring with OFDR, it is necessary to sweep the wavelength in order to measure the backscattered light. This allows us to obtain intensity data that is averaged over the wavelength range swept in the OFDR measurement.

[0044] Here, as shown in Figure 4, if the measurement ranges of two adjacent data points measured with shifted center wavelengths overlap, it means that the averaging effect of one wavelength component is being considered redundantly between the two adjacent data points. Therefore, it cannot be said that the phase difference between cores is sufficiently varied (it cannot be said that the wavelengths in equations (3) to (5) above have been sufficiently varied), and there is a possibility that the statistical characteristics of the power coupling coefficient cannot be measured properly.

[0045] In contrast, by setting the sweep interval so that the sweep range of the wavelength-swept light does not overlap before and after the wavelength change, the statistical characteristics of the power coupling coefficient can be obtained more reliably.

[0046] Returning to Figure 2, in step S3, the measuring device 20 measures the backscattered light using the method described above.

[0047] Here, with reference to Figures 5 and 6, a specific method for measuring backscattered light will be described. Figure 5 is a diagram illustrating the measurement system for the backscattered light intensity from the incident core #1. As shown in Figure 5, when measuring the backscattered light intensity from the incident core #1, wavelength-swept light is incident on the incident core #1 from the measuring device 20, and the backscattered light from the incident core #1 is received by the measuring device 20.

[0048] Figure 6 illustrates the measurement system for backscattered light intensity from adjacent core #2. As shown in Figure 6, when measuring backscattered light intensity from adjacent core #2, wavelength-swept light is incident on the incident core #1 from the measuring device 20, and then the backscattered light from the adjacent core is received by the measuring device 20 via the circulator 31. The same method can be used to measure backscattered light even when the optical fiber 1 under measurement has more adjacent cores.

[0049] Returning to Figure 2, in step S4, the calculation unit 42 repeatedly calculates the power coupling coefficient for each measurement of the measuring device 20 based on the output signal corresponding to the backscattered light intensity from the photodetector 25.

[0050] Specifically, the calculation unit 42 uses the measured backscattered light and the following equation (see Non-Patent Document 1) to determine the power coupling coefficient.

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[0051] Figure 7 shows an example of actual waveform measurement in a two-core fiber. Figure 7 shows an example of measurement for a certain wavelength. By sweeping the wavelength during measurement, measurement results can be obtained for each wavelength. In this embodiment, the power of both cores is considered to be completely coupled at the position indicated by the black dotted line in the figure, and the power coupling coefficient is calculated by substituting the intensity ratio and distance at this position into equation (5). Specifically, in this embodiment, the position for calculating the power coupling coefficient is the position where the power difference between the cores first falls within 0.5 dB. In other words, in this embodiment, the power coupling coefficient is calculated using a power difference of 0.5 dB between the cores as a threshold. To put it another way, the characteristic measurement device 40 calculates the power coupling coefficient at the position where the difference in backscattered light intensity between the cores is below a predetermined threshold.

[0052] Return to Figure 2. In step S5, the characteristic measurement system 100 determines whether or not measurements were taken over the entire wavelength sweep range. This determination process may be performed by either the measuring device 20 or the characteristic measurement device 40.

[0053] If the measurement is not completed across the entire wavelength sweep range (step S5: No), the characteristic measurement system 100 repeats the process from steps S2 to S4. On the other hand, if the measurement is completed across the entire wavelength sweep range (step S5: Yes), the calculation unit 42 calculates the average value and variance of the power coupling coefficient in step S6.

[0054] Figure 8 shows the histogram of the power coupling coefficients measured. Here, the wavelength change width (overall wavelength sweep range) is 42 nm, the wavelength change step (sweep interval) is 0.5 nm, and the OFDR wavelength sweep width (sweep range) is 0.4 nm. In this result, the average value of the power coupling coefficient is 0.36 nm. ―1 The variance is 0.1m ―2 And so it was found.

[0055] The characteristic measuring device of the present invention can also be realized by a computer and a program, and the program can be recorded on a recording medium or provided via a network. The program of this disclosure is a program that causes a computer to realize each function of the device of this disclosure, and is a program that causes a computer to execute each procedure of the method performed by the device of this disclosure. [Industrial applicability]

[0056] This disclosure can be applied to the information and communications industry. [Explanation of Symbols]

[0057] 1: Fiber under measurement 20: Measuring device 21: Wavelength swept light source 22, 24: Coupler 23: Circulator 25:Receiver 30: Optical multiplexer / demultiplexer 31: Circulator 40: Characteristic measuring device 41: Control Unit 42: Arithmetic section 100: Characteristic Measurement System

Claims

1. A measurement device repeatedly measures the backscattered light from at least one core of a coupled multicore fiber while varying the wavelength of the wavelength-swept light, and calculates the power coupling coefficient corresponding to each measured backscattered light. Characteristic measuring device.

2. The statistical characteristics of the power coupling coefficients are calculated from the multiple power coupling coefficients that have been calculated. The characteristic measuring device according to claim 1.

3. The power coupling coefficient is calculated at the position where the difference in backscattered light intensity between cores is below a predetermined threshold. The characteristic measuring device according to claim 1.

4. A characteristic measuring device according to any one of claims 1 to 3, A measurement device that repeatedly measures backscattered light from each core while varying the wavelength of the wavelength-swept light, and injecting it into at least one core of a coupled multicore fiber. Equipped with, Characteristic measurement system.

5. The measuring device performs measurements such that the wavelength sweep range of the wavelength sweep light does not overlap before and after changing the wavelength of the wavelength sweep light. The characteristic measurement system according to claim 4.

6. Wavelength sweep light is injected into at least one core of a coupled multicore fiber while changing its wavelength. The backscattered light from each core is repeatedly measured, Calculate the power coupling coefficient corresponding to each measured backscattered light. Characteristic measurement method.

7. The statistical characteristics of the power coupling coefficients are calculated from the multiple power coupling coefficients that have been calculated. The characteristic measurement method according to claim 6.

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