JP6636273B2 - Connection method of multi-core optical fiber - Google Patents

Description

  The present invention relates to a method for connecting a multi-core optical fiber.

  In order to overcome the limit of the data transmission capacity of a general-purpose single mode optical fiber, the practical use of a multi-core optical fiber having a plurality of cores in one optical fiber is under study. In this multi-core optical fiber, one core is usually provided at the center in the cross section, and a plurality of cores are provided so as to surround the core. Therefore, when connecting the multi-core optical fibers, or when connecting the multi-core optical fiber and the optical component, the alignment is performed so as to reduce the axial deviation of the center core, and further, the axial rotation of the outer core is performed. It is necessary to perform shaft rotation adjustment to reduce the displacement.

  In Patent Document 1, the connection end faces of a pair of multi-core optical fibers are opposed to each other so that the axes are coincident, test light is incident on all the cores from one end of the multi-core optical fiber, and the other multi-core optical fiber is It is disclosed that a test light propagating through a core leaking from a bent portion is detected, and the shaft rotation is adjusted so that the light intensity becomes maximum.

  Patent Document 2 discloses that a multi-core optical fiber faces an optical fiber connecting portion of an optical component, and the multi-core optical fiber is rotated about its axis, and a monitor core detects light reflected from a reflecting portion in the optical fiber connecting portion. It is disclosed that the shaft rotation is adjusted so that the light intensity is maximized.

  Non-Patent Literature 1 discloses that a test light is incident from the side of a bent portion of a first multi-core optical fiber on an incident side, coupled to a core and propagated, and a second multi-core optical fiber on an exit side. It discloses that the test light propagating through the core leaking from the side of the bent portion is detected, and the rotation of the shaft is adjusted so that the light intensity becomes maximum.

JP-A-2015-4762 JP-A-2015-64514

Tanaka, Yawaka, Fujimaki, Taniguchi “Adjustment of Axial Rotation of Multi-core Optical Fiber Connection Using Side Ingress and Emission,” IEICE Technical Report, vol. 113, no. 306, OFT2013-43, pp. 37 -42, November 2013

  In the method of adjusting the rotation of the multi-core optical fiber disclosed in Non-Patent Document 1, test light is incident on the first multi-core optical fiber on the incident side from the side and coupled to the core. A slight displacement of the optical system will lower the coupling efficiency of the test light with the core.

  It is an object of the present invention to provide a method for connecting a multi-core optical fiber that can easily adjust the rotation of the shaft.

  In the method for connecting a multi-core optical fiber according to the present invention, the first and second multi-core optical fibers each having a plurality of cores and a clad covering the plurality of cores are connected to each other so that their connection ends are aligned with each other. While facing each other, test light enters from the side of the first multi-core optical fiber and propagates through the clad, and based on the test light detected from the second multi-core optical fiber, the first and second The axis rotation of the first and second multi-core optical fibers is adjusted so as to reduce the axis rotation deviation of the plurality of cores of the multi-core optical fiber.

  According to the present invention, since the test light is incident from the side of the first multi-core optical fiber and propagates through the clad, the difference in the coupling efficiency between the test light and the clad due to the deviation of the optical system is relatively small, and therefore, The shaft rotation can be easily adjusted.

It is a perspective view of the optical fiber core wire used by the connection method of the multi-core optical fiber concerning an embodiment. FIG. 4 is a diagram showing a step index type refractive index distribution. It is a figure which shows the refractive index distribution of a trench type. It is a figure showing the fusion splicing device used in the connection method of the multi-core optical fiber concerning an embodiment. FIG. 3 is an explanatory diagram illustrating a method of injecting test light into a multi-core optical fiber. It is explanatory drawing which shows the test method of an Example. 6 is a graph illustrating a relationship between a shaft rotation shift and a change amount of optical power of detected test light.

  Hereinafter, embodiments will be described in detail with reference to the drawings.

  In the multi-core optical fiber connecting method according to the embodiment, a pair of multi-core optical fiber core wires 10 as shown in FIG. 1 is used. It is preferable that the pair of multi-core optical fibers 10 have the same configuration.

  The multi-core optical fiber 10 has a multi-core optical fiber 11 and a coating layer 12 that covers the multi-core optical fiber 11. The outer diameter of the multicore optical fiber 10 is, for example, 200 to 700 μm.

  The multi-core optical fiber 11 has a plurality of cores 11a (seven in FIG. 1) and a cladding 11b covering them. As shown in FIG. 2A, the multicore optical fiber 11 may have a step index (SI) type refractive index distribution in which the refractive index distribution in each core 11a is uniform. Further, as shown in FIG. 2B, the multi-core optical fiber 11 may have a trench type refractive index distribution in which a low refractive index layer surrounding each core 11a is provided in a clad 11b. The outer diameter of the multi-core optical fiber 11 is, for example, 100 to 500 μm.

  The seven cores 11a of the multi-core optical fiber 11 illustrated in FIG. 1 include one core 11a provided at the center in the cross section and six cores 11a disposed so as to surround the core. The six outer cores 11a are arranged at regular intervals in the circumferential direction so as to form a regular hexagon centered on the center core 11a in the cross section with respect to the center core 11a. The center-to-center distance between them and the center-to-center distance between the respective cores 11a are equal. Therefore, the seven cores 11a are arranged so as to form an equilateral triangular lattice as a whole in the cross section. The number of cores 11a is not limited to seven, but is, for example, 2 to 50, and may be 19 or 37. The arrangement of the core 11a is not limited to a regular triangular lattice, but may be a square lattice, or may be rotationally symmetric or line symmetric.

  The plurality of cores 11a have a relatively high refractive index in relation to the cladding 11b, and are made of, for example, quartz. Quartz forming the core 11a may be pure quartz, or may be doped with a dopant such as germanium that increases the refractive index of quartz. It is preferable that all of the plurality of cores 11a have the same diameter, for example, 8 to 11 μm. The center-to-center distance between adjacent cores is, for example, 20 to 80 μm. The core 11a preferably operates in a single mode with respect to the wavelength of the signal light, but may operate in a multimode for mode multiplex transmission. In the case of single mode operation, the mode field diameter for light having a wavelength of 1550 nm is, for example, 9 to 15 μm.

  The cladding 11b has a relatively low refractive index in relation to the core 11a, and is made of, for example, quartz or acrylic resin. The quartz forming the cladding 11b may be pure quartz, or may be doped with a dopant such as fluorine which lowers the refractive index of quartz.

  The coating layer 12 is formed of, for example, an ultraviolet-curable urethane acrylic resin, and preferably has a light transmitting property from the viewpoint that the later-described test light enters and / or exits through the coating layer 12. The “light transmittance” means that the transmittance ((light intensity of outgoing light / light intensity of incident light) × 100) after transmitting the thickness of the coating layer 12 is 1% or more at the wavelength of the test light. It means that. Therefore, if the transmittance is 1% or more, the coating layer 12 has light transmittance even if it is colored. The thickness of the coating layer 12 is, for example, 30 to 200 μm.

  The above multi-core optical fiber core 10 can be manufactured by a known method.

  In the multi-core optical fiber connection method according to the embodiment, the coating layer 12 of each connection end of the pair of multi-core optical fibers 10 is peeled off by a predetermined length to expose the multi-core optical fiber 11.

  The exposed length of the exposed multi-core optical fiber 11 is, for example, 2 to 20 mm. The exposed connection end face of the multi-core optical fiber 11 is preferably perpendicular to the axis.

  In the multi-core optical fiber connecting method according to the embodiment, a pair of multi-core optical fiber cores 10 from which the coating layer 12 at the connection end has been peeled is set in the fusion splicing device 20 shown in FIG.

  The fusion splicing device 20 includes a pair of a clamp 21, a guide member 22, and a discharge electrode 23.

  The pair of clamps 21 are arranged at intervals, and hold the multi-core optical fiber core 10 by projecting the portion where the coating layer 12 is peeled off and the multi-core optical fiber 11 is exposed inward. It is configured. Each clamp 21 is configured such that the held multi-core optical fiber core 10 can be moved in the direction in which the clamp 21 is disposed (hereinafter, referred to as “length direction”). Each of the clamps 21 is also configured so that the held multi-core optical fiber core 10 can be axially rotated.

  The pair of guide members 22 are disposed at an interval inside the pair of clamps 21, and have V-grooves 24 extending in the length direction on the respective upper surfaces. Each guide member 22 is configured to project the multi-core optical fiber 11 exposed by peeling off the covering layer 12 protruding from the corresponding clamp 21 and further inwardly project from the guide member 22 to be supported by the V-groove 24. .

  The pair of discharge electrodes 23 are disposed on the left and right sides at the center between the pair of guide members 22 with an interval.

  Note that a CCD camera (not shown) for checking the position of the multi-core optical fiber 11 is provided between the pair of clamps 21 in the fusion splicing device 20.

  In the multi-core optical fiber connection method according to the embodiment, one of the pair of clamps 21 holds one of the pair of multi-core optical fiber core wires 10, and the coating layer 12 at a portion projecting inward from the clamp 21 is peeled off. The exposed first multi-core optical fiber 11 is supported by the corresponding V-groove 24 of the guide member 22. Similarly, the other of the pair of clamps 21 holds the other of the pair of multi-core optical fiber core wires 10, and the second multi-core optical fiber exposed by peeling off the coating layer 12 at the portion protruding inward from the clamp 21. The fiber 11 is supported by the corresponding V groove 24 of the guide member 22. Then, the first and second pair of multi-core optical fibers 11 are moved in the length direction by the clamp 21 so as to protrude from the guide member 22 so that their connection end faces face each other. At this time, the first and second pairs of multi-core optical fibers 11 are supported by the V-grooves 24 of the guide member 22, respectively, so that the connection end faces face each other with their axes aligned. These opposing positions are preferably between the pair of discharge electrodes 23. The distance between the connection end faces of the first and second pair of multi-core optical fibers 11 facing each other is, for example, 5 to 50 μm.

  In the multi-core optical fiber connection method according to the embodiment, the first multi-core optical fiber 11 is set as an incident side, and test light is incident from the side to propagate the clad 11b.

  It is preferable that the test light be incident on the first multi-core optical fiber 11 via the coating layer 12 as shown in FIG. 4 from the viewpoint that the operation is easy because of the strength. In this case, from the viewpoint of making the test light efficiently enter the multi-core optical fiber 11, it is preferable to perform the test by bringing the test light source 31 into contact with the coating layer 12. Further, from the viewpoint of suppressing the absorption of the test light by the coating layer 12, it is preferable that the distance L from the end of the coating layer 12 to the center of the test light source 31 from which the test light is emitted is within 100 mm.

  The test light may be incident on the first multi-core optical fiber 11 from the side of the linearly provided first multi-core optical fiber 11, or the first multi-core optical fiber 11 may be bent. It may be performed from the side of that part. The radius of curvature at the axial position in the bent portion of the multi-core optical fiber 11 is, for example, 5 to 50 mm.

  The test light is not particularly limited. For example, white light may be used. However, in a case where the test light is leaked by bending the second multi-core optical fiber 11 on the emission side as described later, bending may be performed. It is preferable to use near-infrared light (wavelength: 800 to 2500 nm) from the viewpoint of high loss and easy leakage.

  In the multi-core optical fiber connection method according to the embodiment, based on the test light detected from the second multi-core optical fiber 11 on the emission side, the axial rotation shift of the plurality of cores 11a of the first and second multi-core optical fibers 11 is performed. Of the first and second multi-core optical fibers 11 is adjusted so as to reduce.

  The detection of the test light in the second multi-core optical fiber 11 on the emission side may be performed at the end of the other multi-core optical fiber core 10, and the bending of the second multi-core optical fiber 11 on the emission side is given. You may make it leak from the side of a part. In the latter case, the injection of the test light into the first multi-core optical fiber 11 and the detection of the test light from the second multi-core optical fiber 11 can be performed at the position where the fusion splicing device 20 is provided. The property becomes good. The radius of curvature at the axial position in the bent portion of the multi-core optical fiber 11 is, for example, 2.5 to 20 mm. In this case, it is preferable to bend the multi-core optical fiber core 10 covered with the coating layer 12.

  The test light detected from the second multi-core optical fiber 11 on the emission side may be test light propagated in the single mode in the core 11a or test light propagated in the multi-mode in the clad 11b. May be both of them.

  The axis rotation of the first and second multi-core optical fibers 11 is such that when the test light propagating through the core 11a is detected, the overlap between the core 11a and the clad 11b of the first and second multi-core optical fibers 11 is small. In this case, the light intensity is reduced so that the overlap is minimized and the light intensity is minimized. When the test light propagating through the clad 11b is detected, the overlap of the clad 11b of the first and second multi-core optical fibers 11 is increased to increase the light intensity. To maximize the light intensity.

  The shaft rotation of the first and second multi-core optical fibers 11 is performed by the clamp 21. In the shaft rotation adjustment, one of the first and second multi-core optical fibers 11 may be fixed and the other may be rotated. Further, both may be rotated.

  In the multi-core optical fiber connection method according to the embodiment, after adjusting the rotation of the first and second multi-core optical fibers 11, the clamp 21 is used to move the first and / or second pair of multi-core optical fibers 11 in the length direction. By being moved, their connection end faces abut each other, and discharge is performed from the discharge electrode 23 so that they are fusion-spliced.

  By the way, as disclosed in Non-Patent Document 1, when test light is incident from the side of the first multi-core optical fiber and propagates through the core, for example, a slight displacement of an optical system such as a test light source causes a shift of the test light. The coupling efficiency with the core will be reduced. On the other hand, according to the multi-core optical fiber connection method according to the above embodiment, the test light enters from the side of the first multi-core optical fiber 11 and propagates through the clad 11b. The difference in the coupling efficiency between the test light and the clad 11b due to the displacement is relatively small, and therefore, the rotation of the shaft can be easily adjusted.

  Also, as disclosed in Non-Patent Document 1, when test light is incident from the side of the first multi-core optical fiber and propagates through the core, the core is displaced due to the axial misalignment of the first and second multi-core optical fibers. A difference occurs in the light intensity of the test light propagating between each other, and a change in the light intensity causes a difference in a change in the light intensity with respect to the axial rotation deviation. On the other hand, according to the multi-core optical fiber connection method according to the above embodiment, the test light is incident from the side of the first multi-core optical fiber 11 and propagates through the clad 11b. Does not occur.

  Furthermore, as disclosed in Non-Patent Document 1, when test light is incident from the side of the first multi-core optical fiber and propagates through the core, the side of the bent portion of the first multi-core optical fiber is It is necessary to input the test light from. On the other hand, according to the multi-core optical fiber connection method according to the above embodiment, the test light is incident from the side of the first multi-core optical fiber 11 and propagates through the clad 11b. There is no.

(Test method)
FIG. 5 shows a test method in the example. The parts having the same names as those in the above embodiment are denoted by the same reference numerals as those in the above embodiment.

  The first and second multi-core optical fiber cores 10 on the connection side and the first multi-core optical fiber core 10 (3 m in length) on the connected side are subjected to the same operation as in the above-described embodiment to perform the first and second operations. The axial rotation of the first and second multi-core optical fibers 11 included in the multi-core optical fiber 10 was adjusted.

<Example 1>
The first and second multi-core optical fiber core wires 10 have the same configuration as that shown in FIG. 1, the outer diameter is 310 μm, the outer diameter of the multi-core optical fiber 11 is 180 μm, and the diameter of the core 11 a is 9.3 μm. The center-to-center distance between adjacent cores 11a is 45 μm, the mode field diameter for light having a wavelength of 1550 nm is 10.4 μm, and the first and second multi-core optical fibers 11 have a step index (FIG. 2A). Those having a refractive index distribution of SI) type were used. An LED that emits white light is used as the test light source 31, and the distance L from the end of the coating layer 12 to the emission center of the test light in the linearly provided first multi-core optical fiber 10 is 10 mm. Then, a test light source 31 was attached to the outer peripheral surface of the coating layer 12 in contact therewith. The test light is incident from the side of the first multi-core optical fiber 11 via the coating layer 12 and propagates through the cladding 11b, and the detection of the test light from the second multi-core optical fiber 11 is performed by the second multi-core optical fiber. The measurement was performed by measuring the light intensity of the test light propagating through the core 11a as optical power using a power meter 32 provided at the end of the core wire 10.

<Comparative Example 1>
The first multi-core optical fiber core 10 is bent, and test light from the LED of the test light source 31 is incident on the first multi-core optical fiber 11 through the coating layer 12 from the side of the core, and the core 11a is bent. The test light from the second multi-core optical fiber 11 is detected by the power meter 32 provided at the end of the second multi-core optical fiber 10, and the light intensity of the test light propagated through the core 11a is measured by the optical power. The measurement was performed as follows.

<Example 2>
As the first and second multi-core optical fibers 10, the outer diameter is 310 μm, the outer diameter of the multi-core optical fiber 11 is 180 μm, the diameter of the core 11a is 8.2 μm, the center-to-center distance between adjacent cores 11a is 45 μm, And a mode field diameter for light having a wavelength of 1550 nm is 10.3 μm, and the first and second multi-core optical fibers 11 have a trench type refractive index distribution as shown in FIG. The same operation as in Example 1 was performed.

<Comparative Example 2>
The same operation as in Comparative Example 2 was performed except that the first and second multi-core optical fibers 11 having the trench type refractive index distribution used in Example 2 were used.

(Test results)
FIG. 6 shows the relationship between the shaft rotation deviation and the amount of change based on the maximum value of the optical power of the detected test light in Example 1. According to this, the axis rotation deviation angle width (± X °) at which the difference from the minimum value of the optical power was 3 dB or less was ± 1.3 °. In Comparative Example 1, the shaft rotation deviation angle width at which the difference from the maximum value of the optical power was 3 dB or less was ± 6.0 °.

  In Example 2, the axis rotation deviation angle width at which the difference from the minimum value of the optical power was 3 dB or less was ± 2.4 °. In Comparative Example 2, the axis rotation deviation angle width at which the difference from the maximum value of the optical power was 3 dB or less was ± 5.9 °.

  Table 1 shows the above results.

  According to Table 1, Examples 1 and 2 in which the test light was incident from the side of the first multi-core optical fiber 11 and propagated through the clad 11b, showed that the axial rotation deviation was larger than Comparative Examples 1 and 2, respectively. It can be seen that the angle width is narrow. Therefore, in the first and second embodiments, the amount of change in the optical power when the axial rotation shift is small is larger than in the comparative examples 1 and 2, so that the axial rotation of the first and second multi-core optical fibers 11 is large. Adjustment can be performed more easily.

  INDUSTRIAL APPLICATION This invention is useful about the technical field of the connection method of a multi-core optical fiber.

DESCRIPTION OF SYMBOLS 10 Multi-core optical fiber core wire 11 Multi-core optical fiber 11a Core 11b Cladding 12 Coating layer 20 Fusion splicer 21 Clamp 22 Guide member 23 Discharge electrode 24 V-groove 31 Test light source 32 Power meter

Claims (5)

The first and second multi-core optical fibers each having a plurality of cores and a clad covering the plurality of cores are faced with their connection end faces so that their axes coincide, and the first multi-core optical fiber The test light is incident from the side and propagates through the clad, and the axes of the plurality of cores of the first and second multi-core optical fibers are determined based on the test light detected from the second multi-core optical fiber. A method of connecting a multi-core optical fiber that performs axial rotation adjustment of the first and second multi-core optical fibers so as to reduce a rotational displacement,
The first multi-core optical fiber has a light-transmitting coating layer that covers the first multi-core optical fiber,
A method for connecting a multi-core optical fiber, wherein test light is incident on the first multi-core optical fiber from the side via the coating layer. The method for connecting a multi-core optical fiber according to claim 1,
Connecting a multi-core optical fiber that detects test light propagating through the plurality of cores of the second multi-core optical fiber and adjusts the axis rotation of the first and second multi-core optical fibers so that the light intensity is reduced. Method. The method for connecting a multi-core optical fiber according to claim 1,
A method of connecting multi-core optical fibers, comprising detecting test light propagating through the clad of the second multi-core optical fiber and adjusting the rotation of the first and second multi-core optical fibers so that the light intensity is increased. A method for connecting a multi-core optical fiber according to any one of claims 1 to 3,
A method of connecting a multi-core optical fiber, wherein the test light in the second multi-core optical fiber is detected by leaking the test light from a side of a bent portion of the second multi-core optical fiber. A method for connecting a multi-core optical fiber according to any one of claims 1 to 4,
A method for connecting a multi-core optical fiber, wherein the first and second multi-core optical fibers have a trench type refractive index distribution.

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