Optical characteristic measuring system and optical characteristic measuring method

Abstract

The present disclosure provides an optical characteristic measuring system comprising: a first measuring unit that inputs wavelength swept light into one core of a coupled multi-core fiber, and measures both backscattered light in the one core, generated by the wavelength swept light, and backscattered light in at least one other core of the coupled multi-core fiber, excluding the one core, generated by the wavelength swept light; a second measuring unit that measures the wavelength swept light that has been transmitted through the one core, in each of the one core and the other core; a first calculating unit that uses a plurality of backscattered light intensities measured by the first measuring unit to calculate a power coupling coefficient from the one core to the other core; and a second calculating unit that uses a plurality of transmitted light intensities measured by the second measuring unit to calculate spatial mode dispersion in the one core and the other core.

Description

Optical characteristic measuring system and optical characteristic measuring method

[0001] The present disclosure relates to techniques for measuring optical properties of coupled multicore fibers.

[0002] To increase the transmission capacity per optical fiber, research and development of space division multiplexing transmission technology is being conducted. Coupled multicore fibers (MCFs) have attracted attention as a promising transmission medium due to their excellent optical properties, such as low spatial mode dispersion (SMD) and low mode-dependent loss.

[0003] These optical properties are also strongly dependent on the power coupling coefficient, which represents the strength of optical coupling between the cores. Therefore, it is important to measure the power coupling coefficient and various optical properties and understand their mutual relationships.

[0004] Non-Patent Document 1 discloses a measurement method for investigating the relationship between the power coupling coefficient and SMD. In this method, the power coupling coefficient and SMD (low spatial mode dispersion) are measured independently using different measurement systems. Therefore, there is a problem in that measuring both requires the effort and time required to change the measurement system.

[0005] M. Nakamori et al. , “Bending Radius Dependence of Power Coupling Coefficient and Spatial Mode Dispersion in Coupled Multi-Core Fibers”, Prof. OFC, W1C. 1. (2023) Hayashi et al. , “Record-Low Spatial Mode Dispersion and Ultra-Low Loss Coupled Multi-Core Fiber for Ultra-Long-Haul Transmission”, JOURNAL OF LIGHTWAVE TECHNOLOGY, VOL. 35, NO. 3, FEBRUARY 1, 2017, P. 450-457

[0006] In order to solve the above problem, an object of the present disclosure is to make it possible to measure the power coupling coefficient and low spatial mode dispersion without changing the measurement system.

[0007] The present disclosure utilizes transmitted light in measuring the power coupling coefficient to measure spatial mode dispersion.

[0008] The optical characteristic measurement system of the present disclosure includes: a first measurement unit that inputs wavelength swept light into one core of a coupled multicore fiber and measures both backscattered light at the one core generated by the wavelength swept light and backscattered light at at least one other core of the coupled multicore fiber generated by the wavelength swept light; a second measurement unit that measures the wavelength swept light after transmitting through the one core, at the one core and at each of the other cores; a first calculation unit that calculates a power coupling coefficient from the one core to the other core using a plurality of backscattered light intensities measured by the first measurement unit; and a second calculation unit that calculates spatial mode dispersion at the one core and the other core using a plurality of transmitted light intensities measured by the second measurement unit.

[0009] The optical characteristic measuring method of the present disclosure includes: a first measuring unit incidenting wavelength swept light into one core of a coupled multicore fiber, and measuring both backscattered light at the one core generated by the wavelength swept light and backscattered light at at least one other core of the coupled multicore fiber generated by the wavelength swept light; a second measuring unit measuring the wavelength swept light at the one core and at each of the other cores after transmitting through the one core; a first calculating unit calculating a power coupling coefficient from the one core to the other core using the multiple backscattered light intensities measured by the first measuring unit; and a second calculating unit calculating spatial mode dispersion at the one core and the other core using the multiple transmitted light intensities measured by the second measuring unit.

[0010] The first measuring unit may include a delay unit that delays the backscattered light in the other core, and may measure both the backscattered light in the one core and the backscattered light in the other core using a common photodetector.

[0011] The optical property measurement system of the present disclosure may include a spatial mode dispersion transmitting unit that transmits the measurement results of the second measurement unit or the calculation results of the second calculation unit, a spatial mode dispersion receiving unit that receives the measurement results or the calculation results transmitted from the spatial mode dispersion transmitting unit, and a display unit that displays the measurement results or the calculation results received by the spatial mode dispersion receiving unit.

[0012] The above disclosures can be combined as much as possible.

[0013] According to the present disclosure, it is possible to measure the power coupling coefficient and low spatial mode dispersion without changing the measurement system.

[0014] 1 shows an example of a system configuration of this embodiment. 2 shows an example of a measurement method of the present disclosure. 3 shows a state in which a coupled multi-core fiber 90 having two cores is bent at a radius R and twisted at a constant rate in the longitudinal direction. 4 shows the change in the propagation constant difference between cores in the longitudinal direction of a coupled multi-core fiber and the state of the fiber cross section at that time. 5 shows the concept of a method for measuring twist. 6 shows an example of measuring an actual waveform in a coupled multi-core fiber. 7 shows an example of a system configuration of this embodiment. 8 shows an example of a display on a display unit. 9 shows an example of a system configuration of this embodiment. 10 is an explanatory diagram when laying an optical fiber cable. 11 shows an example of a system configuration of this embodiment. 12 shows an example of a system configuration of this embodiment.

[0015] Hereinafter, 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 indicate the same components.

[0016] 1 shows an example of a system configuration of this embodiment. The optical property measurement system of this embodiment includes a first measurement unit 91 and a first calculation unit 92 for observing backscattered light in a coupled multi-core fiber 90, and a second measurement unit 95 and a second calculation unit 96 for observing transmitted light in the coupled multi-core fiber 90.

[0017] The first measuring unit 91 inputs wavelength swept light into one core of the coupled multicore fiber 90, and measures both backscattered light generated by the wavelength swept light at the one core and backscattered light generated by the wavelength swept light at at least one other core excluding the one core of the coupled multicore fiber. The first calculating unit 92 calculates a power coupling coefficient using the multiple backscattered light intensities measured by the first measuring unit 91.

[0018] A second measuring unit 95 measures the wavelength swept light after passing through the one core at the one core and at the other core, and a second calculating unit 96 calculates spatial mode dispersion using the intensities of the transmitted light measured by the second measuring unit 95.

[0019] In this embodiment, the one core corresponding to the incident core is referred to as a "first core," and the other core is referred to as a "second core." The second core is at least one core other than the one core provided in the coupled multicore fiber 90. In this embodiment, an example will be shown in which the second core is one adjacent core adjacent to the first core.

[0020] The fiber to be measured in the present disclosure is a coupled multicore fiber 90, and a first measuring unit 91 and a second measuring unit 95 are connected to first and second cores provided in the coupled multicore fiber 90. Therefore, in this embodiment, an optical multiplexing / demultiplexing unit 93 for connecting the first measuring unit 91 to each core of the coupled multicore fiber 90, and an optical multiplexing / demultiplexing unit 94 for connecting the second measuring unit 95 to each core of the coupled multicore fiber 90 are provided. In this embodiment, an example is shown in which first ports #1 of the optical multiplexing / demultiplexing units 93 and 94 are connected to the first core, and second ports #2 of the optical multiplexing / demultiplexing units 93 and 94 are connected to the second core.

[0021] The first measuring unit 91 is any means capable of measuring the backscattered light intensity in the coupled multicore fiber 90. In this embodiment, an example is shown in which the first measuring unit 91 is a frequency domain reflectometer (OFDR) including a wavelength swept light source 11, an optical circulator 12, and two photodetectors 13 and 14. A first port #1 of the optical multiplexing / demultiplexing unit 93 is connected to the optical circulator 12, and a second port #2 of the optical multiplexing / demultiplexing unit 93 is connected to the photodetector 14.

[0022] The wavelength swept light from the wavelength swept light source 11 is split into two by the optical coupler 15. One of the split lights is input to the coupled multi-core fiber 90 via the optical circulator 12. The other split light is split into two by the optical coupler 16 and supplied to the photodetectors 13 and 14.

[0023] The first branched light from the optical coupler 16 is multiplexed with the backscattered light from the optical circulator 12 by the optical coupler 17. The photodetector 13 receives the multiplexed light from the optical coupler 17. This makes it possible to measure the intensity of the backscattered light output from the first core of the coupled multicore fiber 90.

[0024] The second branched light from the optical coupler 16 is multiplexed by the optical coupler 18 with the backscattered light from the second port #2 of the optical multiplexing / demultiplexing unit 93. The photodetector 14 receives the multiplexed light from the optical coupler 18. This makes it possible to measure the intensity of the backscattered light output from the second core of the coupled multicore fiber 90.

[0025] The first calculation unit 92 acquires the backscattered light intensity in the longitudinal direction of the coupled multicore fiber 90 using the signals received by the photodetectors 13 and 14. The first calculation unit 92 calculates the power coupling coefficient between the first core and the second core in the coupled multicore fiber 90 using the acquired backscattered light intensity.

[0026] The second measuring unit 95 is any means capable of measuring transmitted light from the coupled multicore fiber 90. In this embodiment, an example is shown in which the second measuring unit 95 includes two photodetectors 51 and 52. A first port #1 of the optical multiplexing / demultiplexing unit 94 is connected to the photodetector 51, and a second port #2 of the optical multiplexing / demultiplexing unit 94 is connected to the photodetector 52.

[0027] The photodetector 51 measures the transmitted light output from the first core of the coupled multi-core fiber 90. The photodetector 52 measures the transmitted light output from the second core of the coupled multi-core fiber 90. The second calculation unit 96 calculates the spatial mode dispersion of the coupled multi-core fiber 90 by using the signals received by the photodetectors 51 and 52.

[0028] An example of the optical characteristic measuring method of the present disclosure is shown in Fig. 2. The optical characteristic measuring method of the present disclosure includes steps S11 to S17, by which the power coupling coefficient and spatial mode dispersion are measured.

[0029] In step S11, a core to be measured is set among the cores provided in the coupled multicore fiber 90. For example, a first port #1 of the optical multiplexing / demultiplexing unit 93 is connected to the first core of the coupled multicore fiber 90, and a second port #2 of the optical multiplexing / demultiplexing unit 93 is connected to the second core of the coupled multicore fiber 90. Furthermore, a first port #1 of the optical multiplexing / demultiplexing unit 94 is connected to the first core of the coupled multicore fiber 90, and a second port #2 of the optical multiplexing / demultiplexing unit 94 is connected to the second core of the coupled multicore fiber 90.

[0030] In this embodiment, steps S12 to S15 are repeated after step S11. In step S12, the wavelength of the test light is swept using the wavelength swept light source 11. In step S13, the first measurement unit 91 measures the backscattered light intensity. Specifically, the first measurement unit 91 inputs wavelength swept light into a first core provided in the coupled multicore fiber 90, and measures both the backscattered light at the first core generated by the wavelength swept light and the backscattered light at a second core provided in the coupled multicore fiber 90 generated by the wavelength swept light. In step S14, the second measurement unit 95 measures the transmitted light. Specifically, the second measurement unit 95 measures the wavelength swept light after transmitting through the first core, at each of the first core and the second core. In step S15, it is determined whether all target cores have been measured. For example, if the number of cores in the coupled multi-core fiber 90 is four, it is determined whether backscattered light from the first core and the third core when test light is incident from the first core, and backscattered light from the first core and the fourth core when test light is incident from the first core have been measured. If all of the target cores have not been measured, the process returns to step S11, and step S11 is performed for the unmeasured cores among the target cores. For example, if backscattered light from the fourth core has not been measured, the next step S11 is to connect the second port #2 of the optical multiplexing / demultiplexing unit 94 to the fourth core of the coupled multi-core fiber 90.

[0031] Steps S11 to S13 are repeated until all cores to be measured are measured. Step S14 is performed simultaneously with step S13 in parallel because it uses the wavelength swept light that is incident on the coupled multi-core fiber 90 in step S13. However, step S14 only needs to be performed at least once, and does not have to be performed every time step S13 is performed.

[0032] After all the target cores have been measured (Yes in step S15), steps S16 and S17 are performed. In step S16, the first calculation unit 92 calculates a power coupling coefficient from the first core to the second core in the coupled multicore fiber 90 using the backscattered light intensities of the number obtained in step S13. In step S17, the second calculation unit 96 calculates the spatial mode dispersion at the first core and the second core in the coupled multicore fiber 90 using the transmitted light intensity obtained in step S14. Steps S16 and S17 can be performed simultaneously. Details of steps S16 and S17 will be described below.

[0033] (Step S13) The first measuring unit 91 inputs the wavelength swept light into the first core and measures the intensities of the backscattered light from the first core and the second core. The coupled multi-core fiber 90 may be bent or twisted at a constant rate in the longitudinal direction.

[0034] 3 shows a state in which a coupled multi-core fiber 90 having two cores is bent at a radius R and twisted at a constant rate in the longitudinal direction. When the coupled multi-core fiber 90 is twisted at a constant rate in the longitudinal direction, the cross section of the coupled multi-core fiber 90 rotates with respect to the longitudinal direction. Furthermore, when the coupled multi-core fiber 90 is bent, the refractive index of the first core C1 on the outside and the second core C2 on the inside with respect to the bending radius R changes relatively in the longitudinal direction, and the propagation constant also changes accordingly.

[0035] 4 shows the change in the propagation constant difference between cores in the longitudinal direction of a coupled multi-core fiber 90 and the state (rotation) of the fiber cross section at that time. When the coupled multi-core fiber 90 is twisted at a certain ratio, the propagation constant difference between cores changes periodically. It is known that when the propagation constant difference between cores becomes zero (the propagation constants of each core are the same), light between the cores couples at that point. The points where the difference in propagation constant becomes zero are called phase matching points M1 and M2.

[0036] Fig. 5 shows the concept of a method for measuring twist. For clarity, the radius R and twist are omitted, but in reality, bending and twist are applied as shown in Fig. 3. Consider a coupled multicore fiber 90 including a first core C1 and a second core C2.

[0037] When test light is inserted into the first core C1 from the left side of FIG. 5, the test light propagates from left to right through the first core C1 in FIG. 5. As explained in FIG. 4, there is a region (phase matching point) where the difference in propagation constants between the first core C1 and the second core C2 is zero. Assume there are two phase matching points. At the first phase matching point M1, a portion of the test light propagating through the first core C1 shifts to the second core C2 and travels to the right through the second core C2. The same phenomenon occurs at the second phase matching point M2, where the test light shifts from the first core C1 to the second core C2 and travels to the right in FIG. 5. In this disclosure, the transition of the test light to an adjacent core is defined as optical coupling, and the degree of optical coupling is defined as the power coupling coefficient. The test light propagates through the first core C1 and the second core C2 to the right in FIG. 5. When the test light propagates through the coupled multicore fiber 90, Rayleigh scattering occurs due to particles that are sufficiently small compared to the wavelength and fluctuations in density and composition, and some of this scattering occurs in the opposite direction to the traveling direction of the light, i.e., backscattered light. Since the backscattered light propagates from right to left in Figure 5, backscattered light also occurs in the second core C2 and is output from the end face on the incident side of core C2 in Figure 5.

[0038] (Step S16) The power coupling coefficient h is calculated by multiplying the backscattered light intensity P ｂｓ１ (z) and P ｂｓ２ (z) and the distance z, the following equation can be used (see, for example, Non-Patent Document 1): Here, z is the distance from the optical multiplexing / demultiplexing unit 93 to the coupled multi-core fiber 90 .

[0039] In this embodiment, the backscattered light intensity P ｂｓ１ (z) is the backscattered light intensity P ｂｓ２ (z) can be measured using the signal from the light receiver 14. Therefore, the first calculation unit 92 calculates the backscattered light intensity P ｂｓ１ (z) and P ｂｓ２By applying the ratio of (z) to equation (1), the power coupling coefficient h can be determined.

[0040] 6 shows an example of a measured waveform in the coupled multi-core fiber 90. In FIG. 6, the backscattered light intensity P ｂｓ２ There are two points where there is a large change, which are the phase matching points explained in Figures 4 and 5. Figure 6 shows an example where two phase matching points appear.

[0041] At the phase matching point M2 in FIG. 6, the backscattered light intensities of the cores C1 and C2 are equal, and therefore, it is considered that the power ratio between the first core C1 and the second core C2 is in a steady state at the phase matching point M2, i.e., the powers are completely combined. ｂｓ１ (z) and P ｂｓ２ By substituting the ratio (z) and the distance z into equation (1), the power coupling coefficient h can be calculated.

[0042] (Step S17) In step S14, the wavelength of the test light incident on the coupled multi-core fiber 90 is swept by the wavelength swept light source 11. Therefore, the transmitted light intensity measured by the photodetectors 51 and 52 is expressed as P １ (λ) and P ２ (λ).

[0043] In step S17, the second calculation unit 96 calculates the wavelength dependency of the insertion loss in the coupled multi-core fiber 90 using the following equation: P １ (λ) / (P １ (λ) + P ２ (λ)) (2)

[0044] Spatial mode dispersion can be defined as the square root of the second moment of a time-domain waveform (see, for example, Non-Patent Document 2). Therefore, the second calculation unit 96 converts the wavelength dependence of the insertion loss into frequency dependence, performs an inverse Fourier transform on the frequency dependence of the insertion loss, and converts it into a time-domain waveform. The second calculation unit 96 calculates the square root of the second moment of the obtained time-domain waveform. This allows the spatial mode dispersion to be calculated.

[0045] As described above, the optical characteristic measurement system of this embodiment uses wavelength swept light to measure the power coupling coefficient, and measures the light intensities of the first core and the second core at both ends of the coupled multicore fiber 90, thereby making it possible to measure the power coupling coefficient and spatial mode dispersion of one core all at once.

[0046] Second Embodiment In the above-described embodiment, the first calculation unit 92 that calculates the power coupling coefficient and the second calculation unit 96 that calculates the spatial mode dispersion are installed at the ends of the coupled multicore fiber 90, and are therefore separated from each other. In order to input the test light into the coupled multicore fiber 90, the operator needs to operate the first measurement unit 91. Therefore, in this embodiment, a configuration is provided in which the measurement results output from the first calculation unit 92 and the second calculation unit 96 are collectively displayed on the first measurement unit 91 side.

[0047] 7 shows an example of the system configuration of this embodiment. In addition to the components of the first embodiment, the optical characteristic measurement system of this embodiment includes a spatial mode dispersion transmitter 81, a spatial mode dispersion receiver 82, and display units 83-1 and 83-2. The display unit 83-1 displays the magnitude of the power coupling coefficient calculated by the first calculation unit 92.

[0048] The spatial mode dispersion transmitter 81 transmits the measurement results from the second measuring unit 95 and the calculation results from the second calculating unit 96. The spatial mode dispersion receiver 82 is arranged on the optical multiplexing / demultiplexing unit 93 side of the coupled multicore fiber 90, and receives the measurement results and calculation results transmitted from the spatial mode dispersion transmitter 81. The display unit 83-2 displays the measurement results and calculation results received by the spatial mode dispersion receiver 82.

[0049] In the present disclosure, step S13 for measuring backscattered light and step S14 for measuring transmitted light are performed simultaneously in parallel. At this time, the spatial mode dispersion transmitter 81 transmits spatial mode dispersion data. Therefore, the optical characteristic measurement system of this embodiment can display the measurement results obtained at both ends of the coupled multicore fiber 90 on display units 83-1 and 83-2 installed on the first measurement unit 91 side.

[0050] In the present disclosure, the first measuring unit 91 and the second measuring unit 95 are connected by a coupled multi-core fiber 90. Therefore, in the present embodiment, the spatial mode dispersion transmitter 81 transmits data using the coupled multi-core fiber 90.

[0051] For example, the spatial mode dispersion data calculated by the second calculation unit 96 is converted into signal data. This signal is transmitted through the second core of the coupled multicore fiber 90, and the signal representing the calculation result of spatial mode dispersion is sent to the first measurement unit 91. When transmitting this data, the optical signal output from the wavelength swept light source 11 in the first measurement unit 91 is stopped, and the second port #2 of the optical multiplexing / demultiplexing unit 93 is connected to the spatial mode dispersion receiving unit 82.

[0052] The display units 83-1 and 83-2 may be one display unit. Also, the first calculation unit 92, the spatial mode dispersion receiving unit 82, and the display units 83-1 and 83-2 may be provided in one device. FIG. 8 shows an example of what the display unit displays. The display unit 83 displays graphs of backscattered light intensity and spatial mode dispersion. For example, graphs B1 and B2 of backscattered light intensity are shown, with distance on the horizontal axis and intensity on the vertical axis. B1 shows the backscattered light intensity measured by the optical receiver 13, and B2 shows the backscattered light intensity measured by the optical receiver 14. For example, graph T1 of spatial mode dispersion is shown, with delay time on the horizontal axis and intensity on the vertical axis.

[0053] The display unit 83 also displays the power coupling coefficient calculated using the graphed distance waveforms B1 and B2, and the spatial mode dispersion calculated using the graphed time waveform T1.

[0054] In this embodiment, the measurement results output from the first calculation unit 92 and the second calculation unit 96 can be displayed together on the display unit 83. By setting the spatial mode dispersion transmission unit 81 to transmit data automatically, the measurement results of both the power coupling coefficient and SMD (low spatial mode dispersion) can be automatically displayed on the display unit 83.

[0055] In this embodiment, an example is shown in which the spatial mode dispersion transmission unit 81 transmits both the measurement results from the second measurement unit 96 and the calculation results from the second calculation unit 96, but the present disclosure may also be applicable to either one.

[0056] 9 shows an example of a system configuration of this embodiment. The optical property measurement system of this embodiment includes a third calculation unit 84 in addition to the configuration of the second embodiment. In this embodiment, the configuration arranged on the optical multiplexing / demultiplexing unit 93 side of the coupled multicore fiber 90 in the second embodiment will be referred to as a first measurement device 71, and the configuration arranged on the optical multiplexing / demultiplexing unit 94 side of the coupled multicore fiber 90 in the second embodiment will be referred to as a second measurement device 72.

[0057] The third calculation unit 84 acquires the power coupling coefficient from the first calculation unit 92 and the spatial mode dispersion from the spatial mode dispersion receiving unit 82, and compares them with a reference value. This inputs a value that serves as a reference for the characteristics, and allows comparison with the measurement results of the spatial mode dispersion and the power coupling coefficient. The reference value is a value that satisfies the characteristics of the corresponding coupled optical fiber.

[0058] When an optical fiber cable containing a coupled multi-core fiber 90 is installed outdoors, it may be subjected to unexpected bending. If the coupling between cores in the coupled multi-core fiber 90 becomes unexpected, the optical characteristics will change, and therefore it is necessary to evaluate the optical characteristics of the optical fiber after installing the optical fiber cable. Therefore, in this embodiment, the third calculation unit 84 compares the measurement results with reference values.

[0059] 10 , for example, a first measuring device 71 is connected to the coupled multi-core fiber 90-1 at point A, and a second measuring device 72 is connected to point B, of coupled multi-core fibers 90-1 and 90-2 included in an optical fiber cable 97 laid from point A to point B. Then, measurement of the coupled multi-core fiber 90-1 is performed. After measurement of the coupled multi-core fiber 90-1 is completed, the next coupled multi-core fiber 90-2 is measured.

[0060] In this embodiment, the display unit 83 is provided in the first measuring device 71, so the optical characteristics are displayed at point A and can be compared with a reference value. The reference value is a numerical value that determines whether installation is acceptable or not. If the reference value is met, the worker knows that the optical fiber cable 97 being installed in front of him is installed in the expected condition. On the other hand, if the reference value is not met, he knows that the installation is in an abnormal condition. If the condition is abnormal (unexpected), the distance of the unexpected bend can be found based on the backscattered light intensity and the bend can be corrected. This makes it possible to provide high-quality communication services.

[0061] 11 shows an example of a system configuration of this embodiment. The optical characteristic measurement system of this embodiment differs from the other embodiments in the configuration of the first measurement unit 91. In this embodiment, instead of the two photodetectors 13 and 14, one photodetector 41 and two delay lines 42 and 43 are provided.

[0062] The delay line 43 functions as a delay unit that delays the backscattered light from the second core C2. The first measuring unit 91 measures both the backscattered light from the first core C1 and the backscattered light from the second core C2 using a common photodetector 41.

[0063] The delay line 42 is connected between the optical coupler 15 and the optical coupler 44. The optical coupler 45 is connected between the optical circulator 12 and the optical receiver 41, and the optical coupler 45 is connected to the second port #2 of the optical multiplexing / demultiplexing unit 93. The delay line 43 is connected to the path from the optical multiplexing / demultiplexing unit 93 to the optical coupler 45.

[0064] The backscattered light from the first core C1 is received by the optical receiver 41 via the optical coupler 45 from the optical circulator 12. The backscattered light from the second core C2 is received by the optical receiver 41 via the optical coupler 45. In this embodiment, the backscattered light from the second core C2 is delayed by the delay line 43, so that the backscattered light from the first core C1 passes through the optical coupler 45 first, and then the backscattered light from the second core C2 passes through the optical coupler 45. By matching the length of the delay line 42 to the delay line 43, the backscattered light from the first core C1 can be received by the optical receiver 41, and then the backscattered light from the second core C2 can be received by the optical receiver 41.

[0065] In this embodiment, the backscattered light from the second core C2 is delayed by the delay line, but any other means may be used instead of the delay line.

[0066] 12 shows an example of a system configuration of this embodiment. As shown in FIG. 1 , the optical property measurement system of the present disclosure includes photoreceivers 51 and 52 that receive transmitted light through a coupled multicore fiber 90. Therefore, the optical property measurement system of this embodiment includes a fourth calculation unit 85 that performs calculation processing using signals received by the photoreceivers 51 and 52.

[0067] The fourth calculation unit 85 may calculate, for example, propagation loss and mode-dependent loss other than spatial mode dispersion. However, the fourth calculation unit 85 may process the above parameters in the second calculation unit 96 by expanding the function of the second calculation unit 96.

[0068] In research and development, various tests are conducted, for example, by changing the distance between cores, the refractive index difference between the cores, and the shape of the refractive index profile (e.g., step index type). The reason for this is that the ideal scenario for the coupled multicore fiber 90 is different. For example, optical fibers for data centers are used for wiring inside buildings, so they are short distances. Long-distance optical fibers are used for distances exceeding 1000 km. It is clear that the performance required of optical fibers differs depending on the distance.

[0069] By employing the measurement system of this embodiment, it is possible to collectively measure various characteristics required for evaluating the coupled multicore fiber 90. In other words, it is possible to determine the correlation between important optical couplings and the propagation loss and mode-dependent loss caused by those optical couplings. This is effective because it allows the evaluation of multiple coupled optical fibers with various parameters changed to be completed quickly.

[0070] (Other Embodiments) In the above-described embodiment, a coupled multi-core fiber 90 having two cores has been described. However, the present disclosure also applies to a fiber having three or more cores, because optical coupling between the cores occurs in the same manner. When applying the present technology to the measurement of a coupled multi-core fiber 90 having three or more cores, this can be achieved by replacing the optical multiplexing / demultiplexing units 93 and 94 in Figure 1 with devices corresponding to the number of cores, setting the number of photodetectors 13 and 14 in the first measuring unit 91 in Figure 1 to the same number as the number of cores, and setting the number of photodetectors 51 and 52 in the second measuring unit 95 in Figure 1 to the same number as the number of cores. The measurement flowchart in Figure 2 can be applied.

[0071] 11: Wavelength swept light source 12: Optical circulator 13, 14, 41, 51, 52: Photoreceivers 15, 16, 17, 18, 44, 45: Optical couplers 81: Spatial mode dispersion transmitter 82: Spatial mode dispersion receiver 83, 83-1, 83-2: Display 84: Third calculator 85: Fourth calculator 90: Coupled multicore fiber 91: First measuring unit 92: First calculator 93, 94: Optical multiplexer / demultiplexer 95: First measuring unit 96: Second calculator 97: Cable

Claims

1. An optical characteristic measurement system comprising: a first measurement unit that inputs wavelength swept light into one core of a coupled multicore fiber and measures both backscattered light at the one core caused by the wavelength swept light and backscattered light at at least one other core other than the one core caused by the wavelength swept light in the coupled multicore fiber; a second measurement unit that measures the wavelength swept light after transmitting through the one core at each of the one core and the other core; a first calculation unit that calculates a power coupling coefficient from the one core to the other core using a plurality of backscattered light intensities measured by the first measurement unit; and a second calculation unit that calculates spatial mode dispersion at the one core and the other core using a plurality of transmitted light intensities measured by the second measurement unit.

2. The optical property measurement system according to claim 1, wherein the first measurement unit includes a delay unit that delays the backscattered light at the other core, and measures both the backscattered light at the one core and the backscattered light at the other core using a common photodetector.

3. An optical characteristic measurement system as described in claim 1, comprising: a spatial mode dispersion transmitting unit that transmits the measurement results of the second measurement unit or the calculation results of the second calculation unit; a spatial mode dispersion receiving unit that receives the measurement results or the calculation results transmitted from the spatial mode dispersion transmitting unit; and a display unit that displays the measurement results or the calculation results received by the spatial mode dispersion receiving unit.

4. An optical characteristic measurement method, in which a first measurement unit inputs wavelength swept light into one core of a coupled multicore fiber, and measures both backscattered light at the one core caused by the wavelength swept light and backscattered light at at least one other core other than the one core caused by the wavelength swept light in the coupled multicore fiber; a second measurement unit measures the wavelength swept light after transmitting through the one core at each of the one core and the other core; a first calculation unit calculates a power coupling coefficient from the one core to the other core using the multiple backscattered light intensities measured by the first measurement unit; and a second calculation unit calculates spatial mode dispersion at the one core and the other core using the multiple transmitted light intensities measured by the second measurement unit.

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