Apparatus and method for measuring inter-core crosstalk

Abstract

The purpose of the present disclosure is to make it possible to easily measure inter-core crosstalk without connecting a fiber.　The present disclosure is a method for measuring inter-core crosstalk for an optical fiber that has a plurality of cores. The method is characterized by inputting light into one core of the optical fiber, collimating the output light from each of the cores of the optical fiber to produce parallel light that has respective angular differences, measuring an intensity distribution for an interference waveform for the parallel light, using the interference waveform for the parallel light to independently acquire each of an interference component between the one core and a core of the optical fiber that is different from the one core and a direct-current component that is not the interference component, and using the interference component and the direct-current component to acquire the crosstalk from the one core to the core that is different from the one core.

Description

[Technical field]

[0001] The present invention relates to a measuring device and a measuring method capable of acquiring inter-core crosstalk in an optical fiber having multiple cores. [Background technology]

[0002] In recent years, with the rapid increase in transmission traffic, multicore fiber (MCF) with multiple cores has attracted much attention as a way to increase capacity even further, replacing the single-mode fiber (SMF) currently used in transmission paths. Transmission using MCF allows the transmission capacity to be expanded by the number of cores compared to conventional SMF. On the other hand, in MCF, inter-core crosstalk (XT) limits the transmission capacity, so XT must be suppressed as much as possible. In addition, to evaluate whether the XT of MCF satisfies the desired value, it is necessary to measure the generated XT.

[0003] To measure the XT of an MCF, it is necessary to measure the light intensity emitted from each core and obtain the light intensity ratio between the cores. To measure the light intensity emitted from each core, the power meter method is generally used, in which each core of the MCF is directly fusion-spliced ​​to the SMF. The power meter method has the advantage of a simple configuration, but it requires alignment and connection for each core, and measurement takes time. Therefore, a method that does not require connection between each core of the MCF and the SMF is desirable.

[0004] As a method to eliminate the need to connect each core of the MCF to the SMF, a method has been proposed in which the light emitted from the MCF is measured by an image sensor and XT is obtained from its intensity (Non-Patent Document 1). In this method, the light emitted from the MCF is imaged by a magnifying optical system and measured by an image sensor to measure the electric field intensity distribution in each core independently. This makes it possible to measure XT without connecting to fibers, etc.

[0005] On the other hand, in an image sensor, the sensitivity of each pixel may differ, and even if the intensity of light emitted from each core is the same, the light intensity captured by the image sensor may differ. Therefore, it is necessary to correct the difference in sensitivity of each pixel.

[0006] In addition, since the minimum measurable XT depends on the dynamic range of the image sensor, in Non-Patent Document 1, after measuring the signal light intensity from the reference core, the end face of the reference core is physically masked with light-shielding tape and the emitted light from the other cores is measured. Therefore, even in Non-Patent Document 1, there is a problem that it is not easy to measure XT. [Prior art documents] [Non-patent literature]

[0007] [Non-Patent Document 1] S. Saitoh, Y. Amma, Y. Sasaki, K. Takenaga, and K. Aikawa, “Improved Method for Measuring Inter-Core Crosstalk in Multi-Core Fibers Using a Near-Infrared Camera”, in 2016 European Conference on Optical Communication (ECOC) p728 (2016). Summary of the Invention [Problem to be solved by the invention]

[0008] An object of the present disclosure is to provide a method for easily measuring the XT of a fiber having multiple cores. [Means for solving the problem]

[0009] In this disclosure, we measure the interference light of each core emitted from a fiber with multiple cores, and by analyzing this interference light, we can obtain the XT between the cores.

[0010] Specifically, the inter-core crosstalk measuring device of the present disclosure comprises: A means for irradiating a laser beam into one core of an optical fiber having multiple cores; a means for collimating light emitted from each core of the optical fiber with an angular difference therebetween; an electric field intensity distribution measuring means capable of measuring an intensity distribution of an interference waveform of the parallel light; an interference waveform analysis means for independently acquiring an interference component between the one core and any other core other than the one core provided in the optical fiber and a DC component other than the interference component, using the intensity distribution of the measured interference waveform; a crosstalk analysis means for acquiring crosstalk from the one core to any other core other than the one core, using the interference component and the DC component; The present invention is characterized by having the following.

[0011] Specifically, the method for measuring inter-core crosstalk according to the present disclosure includes the steps of: A method for measuring inter-core crosstalk in an optical fiber having multiple cores, comprising the steps of: Injecting light into one core of the optical fiber; The light emitted from each core of the optical fiber is made parallel with an angle difference. Measuring an intensity distribution of an interference waveform of the parallel light; Using the interference waveform of the parallel light, an interference component between the one core and any other core provided in the optical fiber other than the one core and a direct current component other than the interference component are obtained independently. obtaining crosstalk from the one core to any core other than the one core using the interference component and the DC component; It is characterized by: Effect of the Invention

[0012] In the present disclosure, the XT of a fiber having multiple cores can be obtained without connecting optical fibers and without masking the reference core end face. Therefore, the present disclosure can easily measure the XT of a fiber having multiple cores. [Brief description of the drawings]

[0013] [Figure 1] 1 shows an example of a measurement device according to the present embodiment. [Figure 2A] 1 shows an example of light emitted from a core C1 of a measured optical fiber. [Figure 2B] 1 shows an example of light emitted from a core C2 of the optical fiber to be measured. [Diagram 3] 1 shows an example of a measurement of the electric field intensity distribution of emitted light. [Figure 4] An example of the observed interference fringes is shown. [Diagram 5] 1 shows an example of a two-dimensional spatial frequency spectrum. [Figure 6] An example of the measurement method of this embodiment will be described. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Hereinafter, the embodiments of the present disclosure will be described in detail with reference to the drawings. Note that the present disclosure is not limited to the embodiments shown below. These implementation examples are merely illustrative, and the present disclosure can be implemented in various forms with various modifications and improvements based on the knowledge of those skilled in the art. Note that components with the same reference numerals in this specification and drawings are assumed to indicate the same components.

[0015] 1 shows an example for carrying out the present disclosure. The measurement device of this embodiment includes a laser light generating unit 11, an input core selecting unit 12, a collimating unit 13, an electric field intensity distribution measuring unit 14, and an arithmetic processing unit 15. Using these components, the measurement device of this embodiment executes a method for measuring inter-core crosstalk in a test optical fiber 91 having multiple cores.

[0016] The laser light generating section 11 and the input core selecting section 12 function as a means for inputting laser light into one core of the optical fiber 91 to be measured. The collimator 13 functions as a means for converting the emitted light from each core of the measured optical fiber 91 into parallel light with an angular difference therebetween. The electric field intensity distribution measuring section 14 functions as an electric field intensity distribution measuring means capable of measuring the intensity distribution of the interference waveform of the parallel light.

[0017] The calculation processing unit 15 functions as an interference waveform analysis means and a crosstalk analysis means. The interference waveform analysis means uses the intensity distribution of the measured interference waveform to independently obtain the interference components between the one core and any other core other than the one core provided in the measured optical fiber 91, and the DC components other than the interference components. The crosstalk analysis means obtains crosstalk from the one core to any core other than the one core, using the interference component and the DC component.

[0018] The arithmetic processing unit 15 can be realized by a computer and a program, and the program can be recorded on a recording medium or provided through a network. The program of the present disclosure is a program for realizing a computer as each functional unit of the device according to the present disclosure, and is a program for causing a computer to execute each step of the method executed by the device according to the present disclosure.

[0019] Coherent laser light generated by the laser light generating unit 11 is input to any core of the measured optical fiber 91. Since the measuring device of this embodiment includes the input core selecting unit 12, it can input the laser light to a desired core of the measured optical fiber 19. The output light of the measured optical fiber 91 passes through a collimating unit 13 such as a collimating lens, and is then output to space.

[0020] Here, the collimating unit 13 is any lens that can convert the emitted light into parallel light, and a general-purpose lens that collimates the emitted light of a general-purpose SMF having one core at the center can be used as the collimating unit 13. By disposing this collimating unit 13 at the output end of the measured optical fiber 91, an angle difference occurs in the emitted light from each core.

[0021] 2A and 2B show an example of light emitted from each core of the test optical fiber 91. As shown in FIG. 2A and FIG. 2B, the central axis A of the test optical fiber 91 is F Since the cores C1 and C2 are disposed at a position shifted by a distance d from the central axis A, the emitted light beams L1 and L2 from the cores C1 and C2 that have passed through the collimator section 13 have a central axis A. F An angular difference occurs according to the amount of shift d from the cores C1 and C2 and the focal length f of the collimator unit 13. Here, in Fig. 2A and Fig. 2B, when attention is paid to the components of the emitted light L1 and L2 from each of the cores C1 and C2 that pass through the center of the lens of the collimator unit 13, the angular difference 2θ between the emitted light L1 and L2 from the collimator unit 13 has the following relationship.

number

[0022] The output light L1 and L2 from the collimator unit 13 are measured by an electric field intensity distribution measuring unit 14 such as an image sensor. The measurement of the electric field intensity distribution of the output light is shown in Fig. 3. In Fig. 3, the output light L1 and L2 from each of the cores C1 and C2 overlap with an angular difference, and this intensity distribution is measured on the light receiving surface of the electric field intensity distribution measuring unit 14. Here, since the output light L1 and L2 from each of the cores C1 and C2 are coherent laser beams, the electric field intensity distribution measuring unit 14 can measure the intensity waveform of the interference fringes of the output light L1 and L2.

[0023] In addition, in Figure 2, the central axis A F 3, the optical axis of the collimator 13 is aligned with the central axis A of the fiber 91 to be measured. F The central axis A of the test fiber 91 is the same as that of the test fiber 91.F 1 shows an example in which the light receiving surface of the electric field intensity distribution measuring unit 14 is disposed on the substrate 11, but the present disclosure is not limited to this.

[0024] Consider a case where the measured optical fiber 91 is a four-core fiber having cores C1, C2, C3, and C4, and the input core selection unit 12 inputs laser light only to the core C1. At the output end of the four-core fiber, in addition to the output light from the core C1, the XT component from the core C1 is output from the cores C2, C3, and C4, and the interference fringes of these output lights L1, L2, L3, and L4 are measured.

[0025] Fig. 4 shows an example of interference fringes observed by the electric field intensity distribution measuring unit 14. Fig. 4 shows that the emitted light L1, L2, L3, and L4 from each core C1, C2, C3, and C4 all have the same shape of black solid lines within the observation area of ​​the electric field intensity distribution measuring unit 14 and are measured in an overlapping state.

[0026] In this disclosure, since the emitted light beams L1, L2, L3, and L4 overlap, interference fringes S1, S2, and S3 corresponding to the angle differences between the emitted light beams L1, L2, L3, and L4 can be measured. The intensity waveform I of the measured interference fringes S1, S2, and S3 can be expressed by the following formula.

number

[0027] Here, E1, E2, E3, and E4 are the complex amplitudes of the electric fields of the emitted light from cores C1, C2, C3, and C4. Also, A1, A2, A3, A4 and φ1, φ2, φ3, and φ4 are the amplitudes and initial phases of E1, E2, E3, and E4, respectively. Since E2, E3, and E4 are XT components, their DC components and components due to interference can be ignored, and only the DC component of E1 and the interference component with E1 are observed.

[0028] By applying a two-dimensional Fourier transform to this intensity waveform, a two-dimensional spatial frequency spectrum can be obtained as shown in Figure 5. At the origin of this spectrum, the component I DCAt the position shifted from the origin depending on the angle difference in equation (1), the components of the second, third, and fourth terms, I φ1- φ2 , I φ1-φ3 , I φ1-φ4 From this spatial frequency spectrum, I DC , I φ1-φ2 , I φ1-φ3 , I φ1-φ4 Each component is extracted using a bandpass filter.

[0029] XT from core C1 to cores C2, C3, and C4 respectively 1-2 , XT 1-3 , XT 1-4 Then, the extracted I DC , I φ1-φ2 , I φ1-φ3 , I φ1-φ4 This can be expressed by the following formula:

number

number

number

[0030] Therefore, in the present disclosure, the inter-core XT of an MCF is measured by executing the measurement procedure shown in FIG. 6 using the configuration in FIG. S101. A coherent laser beam is incident on a desired core of the MCF to be measured. S102. Collimate the light emitted from all cores of the MCF and measure the electric field intensity distribution. S103. The measured electric field intensity distribution is subjected to a Fourier transform to extract the DC component and the high frequency component of the spatial frequency corresponding to the angular difference of the emitted light from each core. S104. Obtain XT from the desired core using the extracted components.

[0031] As described above, the present disclosure makes it possible to obtain crosstalk from a core into which light is incident to each of the other cores by using the interference intensity waveform of the output light of the multi-core optical fiber, by making the optical axes of the output light from all the cores of the multi-core optical fiber to be measured have different angles with respect to the light receiving surface of the electric field intensity distribution measuring unit 14. Therefore, the present disclosure makes it possible to easily measure inter-core crosstalk without fiber connection.

[0032] In the above-described embodiment, examples of a two-core optical fiber and a four-core optical fiber in which a core is not arranged on the central axis of the measured optical fiber 91 have been shown, but the present disclosure is not limited thereto. The measured optical fiber 91 of the present disclosure may have a core arranged on the central axis. In this case, the collimator unit 13 converts the light emitted from the core arranged at the center of the measured optical fiber 91 into a parallel light parallel to the central axis of the measured optical fiber 91. This makes it possible to make the optical axes of the light emitted from all the cores provided in the measured optical fiber 91 have different angles from each other. [Industrial Applicability]

[0033] The present disclosure can be applied to the information and communications industry. [Explanation of symbols]

[0034] 11: Laser light generating unit 12: Input core selection section 13: Collimation section 14: Electric field strength distribution measurement section 15: Processing unit 91: Optical fiber under test

Claims

1. A means for irradiating a laser beam into one core of an optical fiber having multiple cores; A means for converting light emitted from each core of the optical fiber into parallel light with an angular difference therebetween; an electric field intensity distribution measuring means capable of measuring an intensity distribution of an interference waveform of the parallel light; an interference waveform analysis means for independently acquiring an interference component between the one core and any other core other than the one core provided in the optical fiber and a DC component other than the interference component, using the intensity distribution of the measured interference waveform; a crosstalk analysis means for acquiring crosstalk from the one core to any other core other than the one core, using the interference component and the DC component; 13. An apparatus for measuring inter-core crosstalk comprising:

2. The inter-core crosstalk measuring device further includes a means for converting light emitted from a core disposed at the center of the optical fiber into parallel light parallel to a central axis of the optical fiber.

2. The inter-core crosstalk measuring device according to claim 1,

3. The interference waveform analysis means Obtaining a two-dimensional spatial frequency spectrum from the interference waveform; obtaining the interference component and the direct current component by extracting frequency components obtained in the two-dimensional spatial frequency spectrum; The inter-core crosstalk measuring device according to claim 1 or 2.

4. The interference waveform analysis means The direct current component is obtained by extracting a frequency component located at the origin obtained in the two-dimensional spatial frequency spectrum; The interference component is obtained by extracting a frequency component located other than the origin obtained from the two-dimensional spatial frequency spectrum. The inter-core crosstalk measuring device according to claim 3 .

5. the interference waveform analysis means performs a two-dimensional Fourier transform on the interference waveform to obtain a two-dimensional spatial frequency spectrum; The inter-core crosstalk measuring device according to claim 3 or 4.

6. A method for measuring inter-core crosstalk in an optical fiber having multiple cores, comprising the steps of: Injecting light into one core of the optical fiber; The light emitted from each core of the optical fiber is made parallel with an angle difference. Measuring an intensity distribution of an interference waveform of the parallel light; Using the interference waveform of the parallel light, an interference component between the one core and any other core provided in the optical fiber other than the one core and a direct current component other than the interference component are obtained independently. obtaining crosstalk from the one core to any core other than the one core using the interference component and the DC component; A method for measuring inter-core crosstalk, comprising:

7. In the inter-core crosstalk measuring method, the outgoing light from a core arranged at the center of the optical fiber is collimated to be parallel to a central axis of the optical fiber; 7. The method for measuring inter-core crosstalk according to claim 6,

Images