MCF connection system and MCF connection method

Abstract

Connects MCF and FIFO easily and with high quality. [Solution] The MCF connection system comprises an MCF transmission path, a first FIFO, a light source that outputs inspection light with different characteristics to one end of the first FIFO, a connection device that optically connects the first end forming one end of the MCF transmission path to the other end of the first FIFO, an identification device that identifies the characteristics of the inspection light output from the second end forming the other end of the MCF transmission path, and a measuring device that measures the first optical power, which is the optical power of the inspection light output from the second end, for each core of the MCF transmission path in correspondence with its characteristics. The light source inputs inspection light to each of the multiple cores at one end of the first FIFO, and the connection device adjusts the optical axis between the other end and the first end of the first FIFO for each core so that the value of each of the first optical powers is within a predetermined range, and after adjusting the optical axis between the other end and the first end of the first FIFO, the connection between the other end and the first end of the first FIFO is fixed.

Description

Technical Field

[0001] The present invention relates to an MCF connection system and the like for connecting between multi-core fibers used in an optical fiber transmission system.

Background Art

[0002] In recent years, with the expansion of international demand for data communication, the importance of submarine cable systems that enable high-capacity and high-speed communication has been increasing. As one means of expanding the transmission capacity without changing the outer diameter of the submarine cable, research and development of multi-core fiber (MCF) has been underway. MCF is an optical fiber that has a plurality of cores in one optical fiber.

[0003] In order to connect a general optical device having an interface of a single-core fiber (SCF) with one core in one optical fiber and an optical transmission line including MCF, fan-in / fan-out (FIFO) is used. General optical devices are, for example, optical repeaters and optical components. FIFO is an optical component having a plurality of SCFs at one end and MCF at the other end, and inside the FIFO, the cores of these SCFs and the cores of MCF are connected. Therefore, FIFO can connect an optical device having an SCF as an interface and MCF.

[0004] In relation to the present invention, Patent Document 1 describes a method for aligning the axes of a coupled multi-core optical fiber. Further, Patent Document 2 describes an MCF provided with markers for aligning the positions of cores.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

[0006] When connecting a FIFO and an MCF, it is preferable that the connection between each core of the FIFO and each core of the MCF be low-loss. Furthermore, it is also preferable that the variation in connection loss between each core of the FIFO and each core in the MCF is small. On the other hand, in a typical procedure for connecting a FIFO and an MCF, multiple beams of light distributed from a single light source are input to one end of the MCF via the FIFO. Then, the optical axis is adjusted between one end of the FIFO and one end of the MCF so that the sum of the optical power output from all cores at the other end of the MCF is maximized.

[0007] However, this procedure has the drawback that it is not easy to know whether each core of the MCF is connected to the FIFO with low loss. This is because the connection status of each core cannot be known at the connection point between one end of the FIFO and one end of the MCF. Therefore, in order to connect the MCF and the FIFO (hereinafter referred to as "the first FIFO") while suppressing variations in connection loss for each core, the following steps (a) to (d) are necessary. (a) Connect a FIFO (first FIFO) to one end of the MCF (first optical axis adjustment). (b) To optimize the connection of the first FIFO, an inspection light is input from the first FIFO and another FIFO (the second FIFO) is connected to the other end of the MCF. (c) Inspection light is input to each core from the second FIFO. (d) Disconnect the connection between the first FIFO and one end of the MCF, and perform a second optical axis adjustment between the first FIFO and one end of the MCF to reduce the variation in connection loss per core.

[0008] In other words, the general procedure requires steps (b)-(d) to disconnect the connection between the first FIFO and the MCF after the connection has been made, and then perform optical axis adjustment using a reverse-direction inspection light. For this reason, it has been difficult to connect the MCF and FIFO easily and with high quality using the general procedure.

[0009] (Purpose of the invention) The present invention aims to provide a technology for easily and with high quality connecting an MCF and a FIFO. [Means for solving the problem]

[0010] The MCF connection system of the present invention is A Multi-Core Fiber (MCF) transmission path with N cores, The first FIFO (Fan-In / Fan-Out), A light source that outputs N inspection lights with different characteristics to one end of the first FIFO, A connecting means for optically connecting a first end forming one end of the MCF transmission line to the other end of the first FIFO, An identification means for identifying the characteristics of the inspection light output from the second end forming the other end of the MCF transmission line, A measuring means for measuring a first optical power, which indicates the optical power of each core of the inspection light output from the second end, for each core of the MCF transmission line in correspondence with the characteristics, Equipped with, N is an integer greater than or equal to 2. The light source inputs the inspection light to each of the multiple cores at one end of the first FIFO. The connecting means adjusts the optical axis between the other end and the first end of the first FIFO for each core so that the respective values ​​of the first optical powers are within a predetermined range, and after adjusting the optical axis between the other end and the first end of the first FIFO, it fixes the connection between the other end and the first end of the first FIFO.

[0011] The MCF connection method of the present invention is An MCF connection method including a first procedure for optically connecting an MCF transmission line having N cores and a first FIFO, where N is an integer of 2 or more, the first procedure includes: inputting inspection light having different characteristics to each of a plurality of cores at one end of the first FIFO, optically connecting each core between the other end of the first FIFO and a first end portion formed by one end of the MCF transmission line, identifying the characteristics of the inspection light output from a second end portion formed by the other end of the MCF transmission line, measuring, for each core of the MCF transmission line, a first optical power indicating the optical power of each core of the inspection light output from the second end portion, in correspondence with the characteristics, adjusting the optical axis between the other end of the first FIFO and the first end portion so that each value of the first optical power is within a predetermined range, fixing the connection between the other end of the first FIFO and the first end portion. The method includes the procedure.

Advantages of the Invention

[0012] The present invention can connect a FIFO and an MCF simply and with high quality.

Brief Description of the Drawings

[0013] [Figure 1] A diagram for explaining an MCF connection system. [Figure 2] A diagram for explaining the optical axis adjustment of an MCF. [Figure 3] An example of a flowchart of the first procedure. [Figure 4] A diagram for explaining an MCF connection system. [Figure 5] An example of a flowchart of the second procedure. [Figure 6] A diagram for explaining an MCF connection system. [Figure 7] A diagram for explaining an MCF connection system. [Figure 8]This is a block diagram showing an example of a light source configuration. [Modes for carrying out the invention]

[0014] Embodiments of the present invention are described below. The arrows in each drawing are provided as examples to illustrate the direction of signals in the embodiments and do not imply any limitation of direction. Furthermore, unless otherwise specified, the intersections of lines do not indicate the combination of signals with different directions. Elements that have been mentioned before are given the same names and reference numerals, and redundant explanations are omitted in each embodiment.

[0015] (First embodiment) This embodiment describes an MCF connection system and an MCF connection method for connecting a FIFO 100 to one end of an MCF transmission line 10. Figure 1 is a diagram illustrating the MCF connection system 1 of the first embodiment of the present invention.

[0016] The MCF transmission line 10 is an optical transmission line composed of MCF. In the MCF transmission line 10, multiple cores are formed inside a single optical fiber. The MCF transmission line 10 is an uncoupled MCF in which each core can transmit light independently. The FIFO 100 is a fan-in / fan-out (FIFO) for connecting the MCF transmission line 10 to multiple SCFs. One end of the FIFO 100 is an MCF (MCF101), and the other end is an SCF (SCF111-114). In the FIFO 100, each core of MCF101 is connected one-to-one with the cores of SCF111-114. That is, the FIFO 100 can connect optical equipment with an MCF interface to optical equipment with multiple SCF interfaces. By connecting the FIFO 100 to one end of the MCF transmission line 10, in an optical transmission system where the MCF transmission line 10 is used as an optical transmission line, optical equipment that uses SCF as an interface (for example, an optical repeater and the optical components provided by the optical repeater) can be connected to the MCF transmission line 10.

[0017] The MCF connection method described in this embodiment will be referred to as the first procedure below. In the first procedure, the FIFO 100 is connected to the MCF transmission line 10. In this embodiment, the case where the MCF transmission line 10 is a 4-core MCF (an MCF with 4 cores 11-14) will be explained as an example. The MCF 101 at one end of the FIFO 100 is also a 4-core MCF, and SCF 111-114 are SCFs. However, the following procedure can also be applied when the MCF transmission line 10 is an N-core MCF, where N is a natural number greater than or equal to 2.

[0018] In Figure 1, the MCF connection system 1 comprises an MCF transmission line 10, a FIFO 100, a light source 500, an optical switch 600, an optical wavelength meter 610, an optical power meter 620, and a connection device 800. The MCF connection system 1 may also include a control device 900. The control device 900 controls the light source 500, the optical switch 600, the optical wavelength meter 610, and the optical power meter 620 in order to perform the first procedure. The control device 900 is one form of control means.

[0019] The light source 500 can output one of four inspection beams with different characteristics. In this embodiment, the case where the characteristic is the wavelength of the inspection beam will be described. That is, the light source 500 outputs four inspection beams with different wavelengths. The number of wavelengths is the number of cores in the MCF transmission line 10. The light source 500 includes laser diodes (LDs) 501-504. LDs 501-504 are, for example, semiconductor laser diodes. The inspection beam with wavelength λ1 output by LD 501 is input to SCF 111 of FIFO 100. Similarly, the inspection beams with wavelengths λ2, λ3, and λ4 output by LDs 502, 503, and 504 are input to SCF 112, 113, and 114, respectively. Since the wavelengths λ1-λ4 of the inspection beams input to SCF 111-114 of FIFO 100 are different, the wavelengths of the inspection beams output from each core of MCF 101 of FIFO 100 are all different. In this embodiment, the light source 500 outputs only one of the four inspection lights with wavelengths λ1-λ4 at a time. That is, the light source 500 outputs an inspection light to one of the SCF111-114. The FIFO 100 and the MCF transmission line 10 are optically connected so that inspection lights with wavelengths λ1 are input to core 11 of the MCF transmission line 10, λ2 to core 12, λ3 to core 13, and λ4 to core 14.

[0020] The connecting device 800 has the function of adjusting the positional relationship between the two MCFs and fixing the connection between them by fusion splicing. Specifically, the connecting device 800 adjusts the optical axis between the MCF 101 and the MCF transmission line 10 so that the cores of both are optically coupled. The core of the MCF 101 and the core of the MCF transmission line 10 are connected by a butt joint during optical axis adjustment and fused together after the optical axis adjustment is completed. A general fusion splicer for fusion splicing two MCFs may be used as the connecting device 800.

[0021] Figure 1 illustrates the case where only LD501 emits light. When the wavelength of the inspection light is λ1, LD502-504 do not participate in optical axis alignment, so these blocks are shown with dashed lines.

[0022] In the procedure of this embodiment, the MCF101 of the FIFO100 and the first end (end 21) forming one end of the MCF transmission line 10 are optically connected for each of the four cores 11-14. At end 21, inspection light with different wavelengths is input from the light source 500 to each of the cores 11-14. As a result, the cores 11-14 of the MCF transmission line 10 each transmit inspection light of different wavelengths. The four inspection lights are output from the cores 11-14 at end 22, which forms the other end of the MCF transmission line 10.

[0023] At end 22, the test light output from cores 11-14 is input to optical switch 600. The optical switch 600 outputs the input test light to optical wavelength meter 610 or optical power meter 620. The optical switch 600 is a 1x2 optical switch capable of outputting light input from the strands (bare fiber) of the MCF transmission line 10 to either of the two SCFs.

[0024] The optical wavelength meter 610 measures the wavelength of the test light input from the optical switch 600 and outputs the measurement result. An optical spectrum analyzer may be used instead of the optical wavelength meter 610. The optical power meter 620 measures the power of the light input from the optical switch 600 and outputs the measurement result. An optical coupler may be used instead of the optical switch 600. The optical coupler, which replaces the optical switch 600, distributes the test light output from end 22 to the optical wavelength meter 610 and the optical power meter 620. By using such an optical coupler, the wavelength and optical power of the input test light can be measured simultaneously.

[0025] Since the light source 500 outputs test light to one of the SCF111-114, only one wavelength of test light is input to the optical wavelength meter 610 and optical power meter 620 at a time. Therefore, the optical wavelength meter 610 and optical power meter 620 measure the wavelength and optical power of the single wavelength of test light output by the light source 500. The method of outputting the measurement results of wavelength and optical power is arbitrary. These measurement results may be displayed on a display or transmitted as data to another device (e.g., control device 900). The optical switch 600 outputs the light input from end 22 to the optical wavelength meter 610 or optical power meter 620. By controlling the optical switch 600 while switching the wavelength of the test light in the light source 500, the wavelength and optical power of the test light propagating through the MCF transmission line 10 can be measured for each core of the MCF transmission line 10.

[0026] Here, the optical axis is adjusted between the FIFO 100 and the MCF transmission line 10 for each core so that the optical power values ​​of each of the four cores measured by the optical power meter 620 fall within a predetermined range. For example, if only the LD 501 emits light from the light source 500 and a test light with wavelength λ1 is input to the core 11 of the MCF transmission line 10, the optical wavelength meter 610 can detect that the wavelength of the test light is λ1. This indicates that the test light output from the LD 501 propagates through the core 11 of the MCF transmission line 10 via the SCF 111 and MCF 101 of the FIFO 100. In other words, the SCF 111 and the core 11 are associated. The optical switch 600 then switches the output destination of the test light from the optical wavelength meter 610 to the optical power meter 620. This allows the optical power meter 620 to measure the optical power of the test light with wavelength λ1 that has propagated through the core 11. Furthermore, the loss in the path from SCF111 through core 11 to end 22 can be determined from the power of the inspection light output by light source 500.

[0027] When the LD outputting the inspection light in the light source 500 is changed from LD501 to LD502, LD503, and LD504, the cores of the MCF transmission line 10 through which the inspection light propagates also change, becoming core 12, core 13, and core 14, respectively. Then, after the wavelength of the inspection light is determined in the wavelength meter 610, the output destination of the inspection light is switched from the wavelength meter 610 to the optical power meter 620. As a result, the optical power of the inspection light output from cores 12-14 and the loss in the path passing through cores 12-14 can be measured in the optical power meter 620 using the same procedure as in the case of core 11. For example, when the light source for the inspection light is switched from LD501 to LD502, inspection light with wavelength λ2 is output from the second core at end 22. Therefore, when the optical wavelength meter 610 detects inspection light with wavelength λ2, it can be determined that the wavelength of the inspection light output by the light source 500 has been switched to λ2, and as a result, the optical power of the inspection light propagating through the core 12 connected to the SCF 112 can now be measured.

[0028] Figure 2 illustrates the optical axis adjustment of the MCF in the connection device 800. The connection device 800 can independently hold the MCF 101 and the MCF transmission line 10. The connection device 800 brings the end of the MCF 101 and the end 21 of the MCF transmission line 10 close together. The connection device 800 then adjusts the optical axis by adjusting the relative positions of each rotation θ around the X, Y, Z axes and the central axis of the MCF 101 and the MCF transmission line 10. By adjusting the optical axis between the MCF 101 and the MCF transmission line 10 for each core according to the optical power of the test light measured in the optical power meter 620, the FIFO 100 and the MCF transmission line 10 can be optically connected with low loss while suppressing variations between cores. If the optical power of the test light output from the MCF101 of the FIFO100 can be considered equal, the difference in optical power between wavelengths of the test light in the optical power meter 620 indicates the difference in core loss from SCF111-114 to end 22. It is preferable that these differences be small. It is also preferable that the connection loss between the FIFO100 and the MCF transmission line 10 be small. That is, it is preferable to adjust the optical axis so that the optical power of the test light at each wavelength measured in the optical power meter 620 is large. Furthermore, if the optical power of the test light at each wavelength output from the MCF101 and the loss at each wavelength of the cores 11-14 of the MCF transmission line 10 are all known, the above optical axis adjustment may be performed using these known values.

[0029] For example, first, the light source 500 is made to output inspection light with wavelength λ1. Then, at the end 21, the optical axis between the MCF 101 and the core 11 is adjusted so that the optical power of the inspection light is increased. After that, the wavelength of the inspection light output by the light source 500 is switched, and the optical axis is adjusted between the MCF 101 and the cores 12-14 for each of the inspection lights with wavelengths λ2, λ3, and λ4. In optical axis adjustment, for example, the positional relationship of each core between the cross-section of the MCF 101 and the cross-section of the end 21 is adjusted. In optical axis adjustment, the rotation angle around the central axis of the MCF 101 and the MCF transmission line 10 may also be adjusted.

[0030] The above optical axis adjustment is performed for the test light with wavelengths λ1 to λ4 in order to suppress variations in optical power among the test light with wavelengths λ1 to λ4 measured by the optical power meter 620. As a result, variations in the connection loss between the cores between the MCF 101 and the end 21 can be suppressed. In other words, the first procedure described in this embodiment has the effect of enabling a simple and high-quality connection between the FIFO 100 and the MCF transmission line 10. This is because, in this procedure, the optical power of the test light is measured for each core 11-14 of the MCF transmission line 10 in correspondence with the characteristics of the test light. Thus, unlike the general procedure, the first procedure can be completed without disconnecting the connection and performing a second optical axis adjustment after the first optical axis adjustment between the FIFO 100 and the end 21 (i.e., with only one optical axis adjustment).

[0031] In this case, a lower limit (first threshold) of the optical power of the test light may be defined for each of the wavelengths λ1-λ4 (i.e., each core), and the optical axis adjustment between the MCF101 and the end 21 may be completed when an optical power of at least the first threshold is measured for all cores. Alternatively, an upper limit (second threshold) of the optical power may be defined for each core, and the optical axis adjustment between the MCF101 and the end 21 may be completed when an optical power of at least the first threshold and at least the second threshold is measured for all cores.

[0032] After optical axis adjustment, the FIFO 100 and the MCF transmission line 10 are fusion-spliced ​​using the connecting device 800. By fusion-splicing the FIFO 100 and the MCF transmission line 10, the FIFO 100 and the MCF transmission line 10 can be integrated. This makes it possible to increase the reliability of the part where the FIFO 100 and the MCF transmission line 10 are connected. Note that methods other than fusion splicing may be applied to connect these two MCFs. For example, the MCF 101 and the MCF transmission line 10 can also be fixed using an adhesive using ultraviolet-curing resin after the optical axis adjustment is completed.

[0033] By following the above procedure, the FIFO 100 and the MCF transmission line 10 can be connected to satisfy the predetermined loss conditions with only one optical axis adjustment. In other words, the MCF connection system 1 of this embodiment can connect the FIFO and the MCF easily and with high quality. Furthermore, during this connection, the optical power of the inspection light can be measured while identifying the cores 11-14 of the MCF connected to the FIFO 100, and the loss of the MCF transmission line 10 can be determined.

[0034] (Another expression of the first embodiment) The effects of the MCF connection system 1 described above can also be obtained by the following configuration. Reference numerals in Figure 1 are enclosed in parentheses. That is, the MCF connection system (1) comprises an MCF transmission line (10) having N cores (where N is an integer of 2 or more), a first FIFO (100), a light source (500), a connection means (800), an identification means (610), and a measurement means (620).

[0035] The light source (500) outputs N inspection lights with different characteristics to one end (SCF111-114) of the first FIFO (100). The connecting means (800) optically connects the first end (21), which forms one end of the MCF transmission line (10), to the other end (101) of the first FIFO (100). The identification means (610) identifies the characteristics (wavelength in the first embodiment) of the inspection light output from the second end (22). The measuring means (620) measures the first optical power, which is the optical power of the inspection light output from the second end (22), for each core (11-14) of the MCF transmission line (10) in correspondence with the characteristics of the inspection light.

[0036] Furthermore, the light source (500) inputs inspection light to each of the multiple cores (SCF111-114) at one end of the first FIFO (100). The connecting means (800) adjusts the optical axis between the other end (MCF101) of the first FIFO and the first end (21) for each core so that the respective values ​​of the first optical power are within a predetermined range.

[0037] Figure 3 is an example of a flowchart for the first step in the above description. In the first step, first, test light is input to each of the multiple cores at one end of the first FIFO (S01 in Figure 3). Each test light has different characteristics. Then, the other end of the first FIFO and the first end are optically connected core by core (S02). The characteristics of the test light output from the second end are identified (S03), and the first optical power is measured in correspondence with the characteristics (S04). Furthermore, the optical axis between the one end and the first end of the first FIFO is adjusted so that each value of the first optical power falls within a predetermined range (S05). Finally, the one end and the first end of the first FIFO are fusion spliced ​​together (S06).

[0038] The MCF connection system 1 and the MCF connection method used therein, as described above, also have the effect of enabling a simple and high-quality connection between the FIFO and the MCF.

[0039] (Second embodiment) Figure 4 illustrates the MCF connection system 2 of the second embodiment. In the second embodiment, the other end (end 22) of the MCF transmission line 10 and the MCF 201 of the FIFO 200 are optically connected core by core. In the second embodiment, the case where the MCF transmission line 10 is a 4-core MCF will also be described. However, the number of cores in the MCF transmission line 10 is not limited to 4 cores.

[0040] The FIFO200 is a fan-in / fan-out connector for connecting an MCF and four SCFs. One end of the FIFO200 is connected to the MCF201, and the other end to the SCF211-214. In the FIFO200, each core of the MCF201 is connected one-to-one with each core of the SCF211-214. In other words, the FIFO200 can connect optical equipment with an MCF interface to optical equipment with multiple SCF interfaces.

[0041] In Figure 4, the optical axis adjustment between the FIFO 100 and the MCF transmission line 10 has been completed. The procedure described in the first embodiment can be applied to this optical axis adjustment. The MCF connection method described in this embodiment will be referred to as the second procedure below. In the second procedure, the optical axis of the end 22 and the MCF 201 is adjusted by the connection device 801 so that the cores of both are optically coupled in their cross-sections. For example, the four cores of the MCF 201 and the four cores 11-14 of the MCF transmission line 10 are optically connected at the end 22 by a butt joint. The function of the connection device 801 is the same as that of the connection device 800 described in Figure 2. That is, the connection device 801 can adjust the optical axis between the MCF 201 and the MCF transmission line 10 so that the cores of both are optically coupled, and can fix the connection between them by fusion splicing after the optical axis adjustment is completed.

[0042] The SCF211-214 of the FIFO200 are input to optical power meters (OPMs) 621-624 via optical band pass filters (OBPFs) 631-634, respectively. Optical band pass filters 631, 632, 633, and 634 are optical filters that transmit only light of wavelengths λ1, λ2, λ3, and λ4, respectively. Optical power meters 621-624 measure the optical power of the light transmitted through optical band pass filters 631-634, respectively. With this configuration, unlike the first embodiment, the MCF connection system 2 can measure the optical power of each test light of wavelengths λ1-λ4 using optical power meters 621-624 without using an optical switch 600.

[0043] Similar to the first embodiment, the light source 500 outputs a test light of one wavelength from wavelengths λ1-λ4. Figure 4 illustrates a case where only LD501 emits light and the power of the test light at wavelength λ1 is measured by the optical power meter 621. When the wavelength of the test light is λ1, LD502-504, optical bandpass filters 632-634, and optical power meters 622-624 do not participate in optical axis adjustment, and these blocks are shown with dashed lines. The optical axis between the end 22 and SCF211-214 is adjusted so that the values ​​of the respective optical powers output from the cores 11-14, as measured by the optical power meters 621-624, fall within a predetermined range. That is, the optical axis of each core between MCF201 and end 22 is adjusted according to the optical power of the test light measured by the optical power meters 621-624. This allows for low-loss optical connection between each core of the MCF201 and the cores 11-14 of the MCF transmission line 10, while suppressing variations in connection loss between cores. For example, by observing the measurements of the optical power meters 621-624 while changing the wavelength of the inspection light and repeatedly adjusting the optical axis between the MCF201 and the end 22 for each core, the optical axis between cores 11-14 and the MCF201 can be adjusted for each core. The procedure for adjusting the optical axis between the MCF101 and the end 21 can be applied mutatis mutandis to adjusting the optical axis between the MCF201 and the end 22. That is, the light source 500 is made to output inspection light with wavelength λ1. Then, the optical axis between core 11 and the MCF201 is adjusted at the end 22 so that the optical power of the inspection light becomes greater. After that, the wavelength of the inspection light output by the light source 500 is switched, and the optical axis is adjusted between the MCF201 and cores 12-14 for each of the inspection lights with wavelengths λ2, λ3, and λ4. In optical axis adjustment, for example, the positional relationship between the cross-section of the MCF201 and the cross-section of the end 22 is adjusted. In optical axis adjustment, the rotation angle around the central axis of the MCF201 and the MCF transmission line 10 may also be adjusted.

[0044] By performing optical axis adjustment between the MCF transmission line 10 and the MCF 201 for each wavelength λ1-λ4, variations in connection loss for each core can be suppressed. In this case, a lower limit (third threshold) of the optical power of the test light may be defined for each core, and the optical axis adjustment between the MCF 201 and the end 22 may be completed when an optical power of at least the third threshold is measured for all cores. Alternatively, an upper limit (fourth threshold) of the optical power may be defined for each core, and the optical axis adjustment between the MCF 201 and the end 22 may be completed when an optical power of at least the third threshold and at least the fourth threshold is measured for all cores.

[0045] By following the above procedure, each core of the FIFO200 and each core of the MCF transmission line 10 can be connected in a manner that satisfies predetermined loss conditions. Furthermore, this connection can be performed by identifying the cores of the FIFO100 and the MCF transmission line 10. This is because, during the optical axis alignment between the end 22 and the MCF201, the core to be connected can be managed based on the wavelength of the inspection light. For example, by setting the transmission wavelength of the optical bandpass filter 631 connected to the SCF211 to wavelength λ1, the path passing through the SCF111 and core 11 can be connected to the SCF211.

[0046] After adjusting the coupling between MCF201 and MCF transmission line 10, the connection between them is fixed using the connection device 801. By fusion splicing MCF201 and MCF transmission line 10, the FIFO200 and MCF transmission line 10 can be integrated while maintaining almost the same level of loss during optical axis adjustment. This enables high reliability of the connection. Furthermore, by performing the procedure of the second embodiment following the procedure of the first embodiment, the FIFO100, MCF transmission line 10, and FIFO200 can be integrated. This allows optical devices using SCF as an interface to be easily connected to both ends of the MCF transmission line 10. Note that methods other than fusion splicing may be applied to connect these two MCFs. For example, the connection between MCF201 and MCF transmission line 10 can also be fixed using an adhesive with UV-curing resin after the optical axis adjustment is complete.

[0047] The MCF connection systems 1 and 2 described in the first and second embodiments, and the first and second procedures applicable thereto, have the effect of enabling easy and high-quality connection of FIFOs to both ends of the MCF. This is because, since the wavelength of the inspection light differs for each core, the optical axis can be adjusted while checking the connection loss for each core when connecting one end (end 21) of the MCF transmission line 10 to the FIFO 100, and when connecting the other end (end 22) of the MCF transmission line 10 to the FIFO 200. As a result, the connection between the FIFO 100 and end 21, and the connection between end 22 and FIFO 200 can be completed with a single optical axis adjustment each, without disconnecting the connection after optical axis adjustment.

[0048] Furthermore, MCFs equipped with markers that serve as a reference for core positioning when fusing MCFs together are also known (for example, Patent Document 2). The markers are used to identify the positions of the multiple cores present in the MCF at both ends of the MCF. However, connecting such an MCF to a FIFO requires a special fusion splicer equipped with a camera for visualizing the markers, and there is also the problem that it can be difficult to identify the cores even with the markers if the number of cores in the MCF is large. However, the MCF connection systems 1 and 2 described in the first and second embodiments connect the FIFO 100 and the MCF transmission line 10 by adjusting the optical axis between the FIFO 100 and the MCF transmission line 10 while identifying each core at both ends (ends 21 and 22) of the MCF transmission line 10 using the wavelength of inspection light. For this reason, markers are not required on the MCF transmission line 10. In addition, the connection devices 800 and 801 do not require any special functions for visualizing the markers on the MCF transmission line.

[0049] (Another way of saying the second step) Figure 5 is an example of a flowchart for the second step. The second step described above can also be written as shown in Figure 5. The reference numerals in Figure 4 are enclosed in parentheses.

[0050] The second step is the MCF connection method, which is performed after the first step. In the second step, first, as in the first step, test light is input to each of the multiple cores (SCF111-114) at one end of the first FIFO (100) (S11 in Figure 5). Each test light has different characteristics. Next, one end (MCF201) of the second FIFO (200) and the second end (22) are optically connected core by core (S12). Then, the characteristics of the test light output from the other end (SCF211-214) of the second FIFO (200) are identified (S13). In addition, the second optical power, which is the optical power of the test light output from the other end (SCF211-214) of the second FIFO, is measured for each core of the MCF transmission line (10) in correspondence with the characteristics of the test light (S14). In this way, the optical axis between the second end (22) and one end of the second FIFO (MCF201) is adjusted so that the values ​​of the second optical powers are within a predetermined range (S15). After the optical axis adjustment is completed, the second end (22) and one end of the second FIFO (MCF201) are fusion spliced ​​together (S16).

[0051] (Modified version of the second embodiment) A modified version of the MCF connection system 2 described above will now be explained. Figure 6 is a block diagram showing an example configuration of the MCF connection system 2A. In the MCF connection system 2A, light source 500A is used instead of light source 500 in the MCF connection system 2.

[0052] The light source 500A comprises an LD510, an optical coupler 511, and optical bandpass filters 512-515. The LD510 is a general-purpose tunable laser diode whose oscillation wavelength is variable. The LD510 outputs light of one of the wavelengths λ1-λ4 as test light under external control. That is, the light source 500A can output test light of any one wavelength from λ1-λ4. The optical coupler 511 distributes the test light output by the LD510 to each core of the FIFO 100. When the FIFO 100 and the MCF transmission line 10 have four cores, the optical coupler 511 is, for example, a 1×4 coupler, and when there are N cores, the optical coupler 511 is, for example, a 1×N coupler. The optical bandpass filters 512, 513, 514, and 515 transmit only light of wavelengths λ1, λ2, λ3, and λ4, respectively. As a result, inspection light of different wavelengths is input to SCF111-114 of FIFO100. Therefore, even when using light source 500A, the wavelengths of the inspection light output from each core of MCF101 of FIFO100 are all different. Even when using light source 500A with such a configuration, the connection procedures between FIFO100 and MCF transmission line 10 and between MCF transmission line 10 and FIFO200, as described in Figures 1 to 5, can be performed.

[0053] Figure 6 illustrates a case where the LD510 emits light at wavelength λ1, and the power of the test light at wavelength λ1 is measured by the optical power meter 631. When the wavelength of the test light is λ1, the optical bandpass filters 513-515, 632-634, and optical power meters 622-624 do not participate in optical axis alignment, and therefore these blocks are shown with dashed lines.

[0054] (Third embodiment) Figure 7 illustrates an MCF connection system 3 according to a third embodiment of the present invention. In this embodiment, the procedure for connecting the end 22 of the MCF transmission line 10 to the FIFO 200 after the end 21 of the MCF transmission line 10 to the FIFO 100 has been connected will be described. The procedure in this embodiment may be carried out in place of the procedure described in the second embodiment. Furthermore, the procedure in the first embodiment may be used for connecting the MCF transmission line 10 to the FIFO 100.

[0055] In the following description, as with previous embodiments, we will describe the case where the MCF transmission line 10 has four cores. However, the following procedure and configuration can also be applied when the MCF has N cores.

[0056] In Figure 7, the MCF connection system 3 includes, in addition to the MCF transmission line 10, FIFOs 100 and 200, a light source 550, an optical switch 601, an optical coupler 651, an optical spectrum analyzer (OSA) 611, and an optical power meter 620.

[0057] The light source 550 includes LD501-504, which are, for example, semiconductor laser diodes. LD501, 502, 503, and 504 each output inspection light with wavelengths λ1, λ2, λ3, and λ4, respectively. Wavelengths λ1-λ4 are distinct from each other. That is, the light source 550 can simultaneously output inspection light with wavelengths λ1-λ4. However, the light source 550 may output inspection light with three or fewer wavelengths from λ1-λ4. Therefore, the light source 550 may be used in place of the light sources 500 and 500A described in the first and second embodiments.

[0058] Prior to the procedure of this embodiment, the MCF101 of the FIFO100 and the end 21 of the MCF transmission line 10 are optically connected to each of the four cores. As a result, at the end 21, inspection light with different wavelengths is input from the light source 500 to each of the four cores 11-14 of the MCF transmission line 10. This causes inspection light of different wavelengths to propagate simultaneously in the cores 11-14 of the MCF transmission line 10. The four inspection lights are output from the cores 11-14 at the other end 22 of the MCF transmission line 10.

[0059] The cores of MCF201 and cores 11-14 of MCF transmission line 10 are optically connected by a butt joint. The light output from the four SCF211-214 of FIFO200 is input to the optical spectrum analyzer 611 and optical power meter 620 via the optical switch 601 and optical coupler 651. The optical switch 601 is a 4x1 optical switch and connects one SCF selected from SCF211-214 to the optical coupler 651. The optical coupler 651 is a 1x2 optical coupler and distributes the light input from the optical switch 601 to the optical spectrum analyzer 611 and optical power meter 620. The optical spectrum analyzer 611 measures the wavelength of the test light of the core selected by the optical switch 601. That is, the optical switch 601 selects the core for which to measure the wavelength and optical power of the test light. The optical power meter 620 measures the optical power of the test light of the core selected by the optical switch 601.

[0060] With this configuration, one of the four test beams output from the FIFO200's SCF211-214 is input to the optical spectrum analyzer 611 and the optical power meter 620 via the optical switch 601 and the optical coupler 651.

[0061] The procedure of the second embodiment can be applied to adjust the optical axis between the end 22 of the MCF transmission line 10 and the MCF201 of the FIFO200. That is, the optical axis is adjusted between the end 22 and the MCF201 so that the optical power values ​​measured by the optical power meter 620 fall within a predetermined range for each of the wavelengths λ1-λ4. By setting the light source 550 to simultaneously output inspection light of wavelengths λ1-λ4, the wavelength and optical power of the inspection light of wavelengths λ1-λ4 can be easily and repeatedly measured using the optical spectrum analyzer 611 and the optical power meter 620. Here, the switching of the wavelength of the inspection light is performed only by switching the optical switch 601. Then, by repeatedly adjusting the optical axis between the MCF201 and the end 22 for each core, the optical axis between the FIFO200 and the MCF transmission line 10 for each core can be suitably adjusted for cores 11-14. In this embodiment, as in the second embodiment, the cores 11-14 of the MCF transmission line 10 and each core of the MCF 201 can be optically connected with low loss while suppressing variations in connection loss between cores.

[0062] (Modified version of the third embodiment) A modified version of the MCF connection system 3 described above will now be explained. Figure 8 is a block diagram showing an example configuration of light source 550A that can be used in place of light source 550 in the MCF connection system 3.

[0063] The light source 550A comprises an ASE (Amplified Spontaneous Emission) light source 520, an optical coupler 521, and optical bandpass filters 522-525. The ASE light source 520 outputs broadband light (ASE light) with a nearly flat spectrum. ASE light can be generated by injecting excitation light into an optical amplification medium. The wavelength band of the ASE light includes the wavelengths λ1-λ4 of the inspection light.

[0064] The optical coupler 521 distributes the ASE light output by the ASE light source 520 to each core of the FIFO 100. When the FIFO 100 and the MCF transmission line 10 have four cores, the optical coupler 521 is a 1×4 coupler, and when there are N cores, the optical coupler 521 is a 1×N coupler. The optical bandpass filters 522, 523, 524, and 525 transmit only light with wavelengths λ1, λ2, λ3, and λ4, respectively. This simultaneously generates inspection light with wavelengths λ1, λ2, λ3, and λ4 from the ASE light. When the SCF111-114 of the FIFO 100 are connected to the light source 550A, inspection light with wavelengths λ1-λ4 is input to the SCF111-114, respectively. An optical attenuator may be connected in series with the optical bandpass filters 522-525. The attenuation amount of the optical attenuator may be set so that the optical power of the test light of each wavelength output from the light source 550 becomes equal.

[0065] Light source 550A generates inspection light using ASE generated by ASE light source 520 and optical bandpass filters 522-525. Therefore, when changing the wavelength of the inspection light, it is only necessary to change the transmission band of optical bandpass filters 522, 523, 524, and 525, and there is no need to change expensive components such as laser diodes.

[0066] Even when using light source 550A, the wavelengths of the inspection light output from each core of the MCF101 of FIFO100 are all different. The first and second steps described in the above embodiment can also be performed using light source 500A, which has such a configuration.

[0067] (Fourth embodiment) In the first to third embodiments, the core of the MCF transmission line 10 through which the inspection light propagated could be identified by the difference in the wavelength of the inspection light. However, the characteristics of the inspection light used for core identification are not limited to wavelength. For example, the four inspection lights input to the SCF111-114 of the FIFO100 may each be pulse-width modulated with different widths. For example, the inspection lights input to the four cores 11-14 of the MCF transmission line 10 may be modulated to have different pulse widths W1-W4, and an optical receiver capable of identifying the pulse width of an optical signal may be used instead of the optical wavelength meter 610 and optical spectrum analyzer 611. The optical receiver can then identify the core through which the inspection light propagated by determining which of W1-W4 the pulse width of the received inspection light is. In other words, even when the characteristic of the inspection light is the pulse width of the inspection light, the core can be identified in the same way as when the characteristic of the inspection light is the wavelength.

[0068] Alternatively, the inspection light may be pulsed light, and the transmission interval of the pulsed light may be varied for each core. For example, the inspection light may be a pulse train, and inspection light with different pulse intervals T1-T4 may propagate through each core. In this case, instead of an optical wavelength meter and an optical spectrum analyzer, an optical receiver capable of identifying the reception interval of the optical pulses is used. Such an optical receiver can identify the core through which the inspection light propagated by determining whether the reception interval of the received inspection light pulse is T1-T4. In other words, even when the characteristic of the inspection light is the pulse interval of the inspection light, the core can be identified in the same way as when the characteristic of the inspection light is the wavelength or pulse width.

[0069] The modulation method for the inspection light is not limited to pulse width or pulse interval. For example, the pulsed light may be amplitude-modulated with a low-frequency signal between 10 kHz and 1 MHz. The modulation frequency may be changed for each core, and the core through which the inspection light propagated may be identified by detecting the frequency of the low-frequency signal with an optical receiver.

[0070] Furthermore, when the inspection light is pulsed light, it is preferable to modulate the inspection light so that the duty cycle of each inspection light propagating through cores 11-14 is the same. This prevents the difference in optical power of the inspection light between cores 11-14 from being affected by the duty cycle when measuring optical power.

[0071] Furthermore, some or all of the above embodiments may also be described as follows, but are not limited to these.

[0072] (Note 1) A Multi-Core Fiber (MCF) transmission path with N cores, The first FIFO (Fan-In / Fan-Out), A light source that outputs N inspection lights with different characteristics to one end of the first FIFO, A connecting means for optically connecting a first end forming one end of the MCF transmission line to the other end of the first FIFO, An identification means for identifying the characteristics of the inspection light output from the second end forming the other end of the MCF transmission line, A measuring means for measuring the first optical power, which represents the optical power of each of the N cores of the inspection light output from the second end, for each core of the MCF transmission line in correspondence with the characteristics, An MCF connection system comprising, N is an integer greater than or equal to 2. The light source inputs the inspection light to each of the multiple cores at one end of the first FIFO. The connecting means adjusts the optical axis between the other end and the first end of the first FIFO for each core so that the respective values ​​of the first optical powers are within a predetermined range, and after adjusting the optical axis between the other end and the first end of the first FIFO, fixes the connection between the other end and the first end of the first FIFO. MCF connection system.

[0073] (Note 2) One end of the first FIFO is a plurality of SCFs (Single Core Fibers) provided by the first FIFO. The other end of the first FIFO is the MCF provided by the first FIFO. The MCF connection system described in Appendix 1.

[0074] (Note 3) It also features a second FIFO, The connecting means optically connects the second end and one end of the second FIFO, The measurement means measures the second optical power, which is the optical power of the plurality of test lights output from the other end of the second FIFO, for each core of the MCF transmission line in correspondence with the characteristics. The connecting means adjusts the optical axis between the second end and one end of the second FIFO so that the respective values ​​of the second optical powers are within a predetermined range. The MCF connection system described in Appendix 2.

[0075] (Note 4) One end of the second FIFO is the MCF provided by the second FIFO, The other end of the second FIFO is one of the multiple SCFs provided by the second FIFO. The MCF connection system described in Appendix 3.

[0076] (Note 5) An MCF connection system as described in any one of Appendix 1 to 4, further comprising control means for controlling the light source, the connection means, the identification means, and the measuring means.

[0077] (Note 6) The aforementioned characteristic is the wavelength of the inspection light, as described in any one of Appendix 1 to 5, for the MCF connection system.

[0078] (Note 7) The aforementioned characteristic is the pulse width of the inspection light, as described in any one of Appendix 1 to 5 of the MCF connection system.

[0079] (Note 8) The aforementioned characteristic is the duty cycle of the pulse of the inspection light, as described in any one of Appendix 1 to 5 of the MCF connection system.

[0080] (Note 9) An MCF connection method comprising a first step for optically connecting an MCF transmission line having N cores to a first FIFO, N is an integer greater than or equal to 2. The first procedure described above is, By inputting inspection light having different characteristics to each of the multiple cores at one end of the first FIFO, The other end of the first FIFO and the first end forming one end of the MCF transmission line are optically connected for each core. Identify the characteristics of the inspection light output from the second end forming the other end of the MCF transmission line. The first optical power, which represents the optical power of each of the N cores of the inspection light output from the second end, is measured for each core of the MCF transmission line in correspondence with the characteristics. The optical axis between the other end of the first FIFO and the first end is adjusted so that each of the first optical power values ​​falls within a predetermined range. The connection between the other end of the first FIFO and the first end is fixed. MCF connection method.

[0081] (Note 10) One end of the first FIFO is a plurality of SCFs (Single Core Fibers) provided by the first FIFO. The other end of the first FIFO is the MCF provided by the first FIFO. The MCF connection method described in Appendix 10.

[0082] (Note 11) An MCF connection method comprising a second step performed after the first step, The second step described above is: One end of the second FIFO and the second end are optically connected for each core. Identify the characteristics of the inspection light output from the other end of the second FIFO, The second optical power, which is the optical power of the inspection light output from the other end of the second FIFO, is measured for each core of the MCF transmission line in correspondence with the characteristics. The optical axis between the second end and one end of the second FIFO is adjusted so that each of the values ​​of the second optical power falls within a predetermined range. The connection between the second end and one end of the second FIFO is fixed. The MCF connection method described in Appendix 9 or 10, including the above.

[0083] (Note 12) One end of the second FIFO is the MCF provided by the second FIFO, The other end of the second FIFO is one of the multiple SCFs provided by the second FIFO. The MCF connection method described in Appendix 11.

[0084] (Note 13) The MCF connection method described in Appendix 11 or 12, wherein at least one of the first and second steps is controlled by a control means.

[0085] (Note 14) The aforementioned characteristic is the wavelength of the inspection light, as described in any one of the appendices 9 to 13, for the MCF connection method.

[0086] (Note 15) The MCF connection method described in any one of the appendices 9 to 13, wherein the characteristic is the pulse width of the inspection light.

[0087] (Note 16) The MCF connection method described in any one of the appendices to 13, wherein the aforementioned characteristic is the duty cycle of the pulse of the inspection light.

[0088] Although the present invention has been described above with reference to embodiments, the present invention is not limited to the above embodiments. Various modifications to the structure and details of the present invention can be made, as can be understood by those skilled in the art within the scope of the present invention.

[0089] For example, some or all of the operation of the MCF connection system in each embodiment may be programmed. The MCF connection system in each embodiment may include a computer that executes this program. The computer may implement some or all of the functions of the MCF connection system in each embodiment by executing the program. The computer may be, for example, a logic device, a central processing unit, or a digital signal processing unit. The control device 900 described in the embodiment may include a computer. At least one of the first and second steps may be controlled by the control unit 900. The program may also be recorded on a computer-readable, fixed, non-temporary recording medium. The recording medium may be, for example, a flexible disk, a fixed magnetic disk, or a non-volatile semiconductor memory. The program may be distributed over a network.

[0090] Furthermore, the configurations described in each embodiment are not necessarily mutually exclusive. The operation and effects of the present invention may be achieved by a configuration that combines all or part of the above-described embodiments. [Explanation of symbols]

[0091] 1, 2, 2A, 3 MCF connection system 10 MCF transmission road 11-14 Core 21, 22 End 100, 200 FIFO 101, 201 MCF 500, 500A, 550, 550A light source 501-504 Laser Diode (LD) 511, 521 Optical coupler 512-515, 522-525 Optical bandpass filters (OBPF) 520 ASE light source 600, 601 Optical switches 610 Optical wavelength meter 611 Optical Spectrum Analyzer (OSA) 620-624 Optical Power Meter (OPM) 631-634 Optical bandpass filters 651 Optical Coupler 800, 801 Connection device 900 Control Unit

Claims

1. A Multi-Core Fiber (MCF) transmission line with N cores, The first FIFO (Fan-In / Fan-Out), A light source that outputs N inspection lights with different characteristics to one end of the first FIFO at different timings, A connecting means for optically connecting a first end forming one end of the MCF transmission line to the other end of the first FIFO, An identification means for identifying the characteristics of the inspection light output from the second end forming the other end of the MCF transmission line, The system includes a measuring means for measuring a first optical power, which represents the optical power of each of the N cores of the inspection light output from the second end, for each core of the MCF transmission line in correspondence with the characteristics, N is an integer greater than or equal to 2, The light source inputs the inspection light to each of the multiple cores at one end of the first FIFO. The connection means adjusts the optical axis between the other end and the first end of the first FIFO for each core so that the respective values ​​of the first optical powers are within a predetermined range, and after adjusting the optical axis between the other end and the first end of the first FIFO, fixes the connection between the other end and the first end of the first FIFO.

2. One end of the first FIFO is a plurality of SCFs (Single Core Fibers) provided by the first FIFO. The other end of the first FIFO is the MCF provided by the first FIFO. The MCF connection system described in claim 1.

3. Furthermore, equipped with a second FIFO, The connecting means optically connects the second end and one end of the second FIFO, The measurement means measures the second optical power, which is the optical power of the inspection light output from the other end of the second FIFO, for each core of the MCF transmission line in correspondence with the characteristics. The connecting means adjusts the optical axis between the second end and one end of the second FIFO so that the respective values ​​of the second optical powers are within a predetermined range, and after adjusting the optical axis between the second end and one end of the second FIFO, fixes the connection between the second end and one end of the second FIFO. The MCF connection system described in claim 2.

4. One end of the second FIFO is the MCF provided by the second FIFO, The other end of the second FIFO is one of the multiple SCFs provided by the second FIFO. The MCF connection system described in claim 3.

5. The MCF connection system according to any one of claims 1 to 4, further comprising control means for controlling the light source, the connection means, the identification means, and the measurement means.

6. The MCF connection system according to any one of claims 1 to 5, wherein the characteristic is the wavelength of the inspection light.

7. The MCF connection system according to any one of claims 1 to 5, wherein the characteristic is the pulse width of the inspection light.

8. The MCF connection system according to any one of claims 1 to 5, wherein the characteristic is the duty cycle of the pulse of the inspection light.

9. An MCF connection method comprising a first step for optically connecting an MCF transmission line having N cores to a first FIFO, N is an integer greater than or equal to 2, The first step described above is, Inspection light with different characteristics is input to each of the multiple cores at one end of the first FIFO at different timings. The other end of the first FIFO and the first end forming one end of the MCF transmission line are optically connected for each core. The characteristics of the inspection light output from the second end forming the other end of the MCF transmission line are identified. The first optical power, which represents the optical power of each of the N cores of the inspection light output from the second end, is measured for each core of the MCF transmission line in correspondence with the characteristics. The optical axis between the other end of the first FIFO and the first end is adjusted so that each of the first optical power values ​​falls within a predetermined range. To fix the connection between the other end of the first FIFO and the first end, MCF connection method.

10. One end of the first FIFO is a plurality of SCFs (Single Core Fibers) provided by the first FIFO. The other end of the first FIFO is the MCF provided by the first FIFO. The MCF connection method described in claim 9.

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