JP2012203036A - Optical transmission line - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical transmission line that easily dissolves accumulation of group speed dispersion using a multi-core fiber.SOLUTION: The optical transmission line is formed by connecting a plurality of multi-core fibers 10 each having a clad 20 and a plurality of cores 31, 32 to each other, the plurality of cores being first cores 31 having normal group speed dispersion and second cores 32 having abnormal group speed dispersion. The second cores are arranged at positions rotationally symmetrical with the first cores about a fiber center axis as an axis of rotation, and the multi-core fibers are connected to each other such that the first cores and second cores abut against each other on a connection plane.

Description

  The present invention relates to an optical transmission line, and more particularly to an optical transmission line in which a plurality of multi-core fibers are connected to each other.

  In recent years, optical fibers have been used in large quantities in various applications such as communication and energy transmission. In particular, optical fibers have been used as communication data paths for transmitting large amounts of data in a short time, and the amount of use has been dramatically increased by removing the conductive wires.

As described above, communication optical fibers are required to be able to transmit and receive more data with a single fiber. Therefore, a multi-core fiber is being studied in which a plurality of cores are put in one optical fiber and a separate signal can be sent in each core. (For example, non-patent documents 1 and 2)
In addition, optical fibers for communication are laid for a long distance and are used for communication with various parts of the world.

JP 2004-56307 A

Takenaga et al., 2010 IEICE Communication Society, BS-6-6 (2010) M.Koshiba, et al., IEICE Electronics Express., 6,98-103 (2009)

  However, in a single mode fiber used as an optical fiber for normal communication, the wave velocity (group velocity) varies depending on the wavelength, so that group velocity dispersion exists and a signal waveform is deformed. Since the group velocity dispersion is accumulated in proportion to the transmission distance, the transmission characteristic is greatly deteriorated in the optical signal transmission using the long-distance optical fiber. In order to deal with this problem, as disclosed in Patent Document 1, it has been proposed to use a dispersion compensating fiber, but a dispersion compensating fiber in a multi-core fiber has not been studied yet.

  The present invention has been made in view of this point, and an object of the present invention is to provide an optical transmission line that can easily eliminate the accumulation of group velocity dispersion using a multi-core fiber.

  The optical transmission line of the present invention is formed by connecting a plurality of multi-core fibers each having a clad and a plurality of cores, and the plurality of cores includes a first core whose group velocity dispersion is normal dispersion, A second core whose group velocity dispersion is anomalous dispersion, and the second core is disposed at a rotationally symmetric position of the first core with a fiber central axis as a rotation axis, The multi-core fibers have a configuration in which the first core and the second core are in contact with each other on the connection surface. Here, the second core is disposed at a rotationally symmetric position of the first core with the fiber center axis as the rotation axis. The first core has the fiber center axis as the rotation axis. By rotating, it moves to the position where the second core before rotation exists.

  The optical transmission line of the present invention is a multi-core in which a first core with normal group dispersion and a second core with anomalous dispersion are overlapped when rotated around the fiber center axis. Because multiple fibers are used, the first core and the second core can be connected by simply rotating one of the fibers around the central axis when connecting multi-core fibers. This makes dispersion compensation easy. Can be done.

2 is a diagram illustrating an end face of a multi-core fiber according to Embodiment 1. FIG. It is a figure which shows the end surface of the multi-core fiber which concerns on Embodiment 2. FIG. 6 is a diagram illustrating an end face of a multi-core fiber according to Modification 1 of Embodiment 2. FIG. 6 is a diagram illustrating an end face of a multicore fiber according to a second modification of the second embodiment. FIG. It is a figure which shows the end surface of the multi-core fiber which concerns on Embodiment 3. FIG. FIG. 10 is a diagram illustrating an end face of a multicore fiber according to a modification of the third embodiment.

  Before describing embodiments of the present invention, the meanings of terms used in the present invention will be described.

  In the present invention, the dispersion parameter D (ps / nm / km) is used as an amount representing the magnitude of group velocity dispersion. The group velocity dispersion is normal dispersion when the dispersion parameter is a negative value, and the abnormal dispersion is when the dispersion parameter is a positive value.

  The group velocity dispersion slope is a change rate of the dispersion parameter D of the group velocity dispersion with respect to the change of the wavelength λ, dD / dλ.

  Moreover, it is preferable to arrange | position a 2nd core next to a 1st core in a multi-core fiber, and to arrange | position a 1st core next to a 2nd core. This relationship is expressed as that the second core is adjacent to and close to the first core, and the first core is adjacent to and close to the second core.

  The second core is adjacent to and adjacent to the first core because when there are a plurality of cores around one first core, That is, the closest core is the second core. Replacing the words "first" and "second" will explain the latter half of each sentence in the previous paragraph. There may be a plurality of cores closest to one core. In this case, a core having an inter-core distance of 1.1 times or less of the shortest inter-core distance is also set to the closest position due to fiber manufacturing variations and the like.

  Next, embodiments of the present invention will be described in detail with reference to the drawings. In the following drawings, components having substantially the same function are denoted by the same reference numerals for the sake of brevity.

(Embodiment 1)
As shown in FIG. 1, the multicore fiber 10 according to the first embodiment includes six first cores 31, 31,... And six second cores 32, 32,. There are a total of 12 cores. In addition, in order to distinguish the first core 31 and the second core 32 in the drawing, the first core 31 is blacked out in terms of expression in the drawing, but actually the first core 31 is not black. Absent. The same expression is used in the following drawings.

  The twelve first cores 31, 31,... And the second cores 32, 32,. Two first cores 31 and 31 are arranged next to each other, and second cores 32 and 32 arranged in pairs are arranged next to each other to form a regular dodecagon. .

  In the first cores 31, 31,..., The group velocity dispersion is normal dispersion (dispersion parameter is negative), and the second cores 32, 32,... Are abnormal dispersion (dispersion parameter is positive). Each of the cores 31 and 32 has a refractive index higher than that of quartz by being doped with quartz or the like. If the dispersion parameter of the first cores 31, 31,... Is -D (ps / nm / km), the dispersion parameter of the second cores 32, 32, ... is D (ps / nm / km). ing. In other words, the first cores 31, 31,... And the second cores 32, 32,. The fact that the absolute values of the dispersion parameters are equal does not mean that they are mathematically strictly equal, but the variations in the structure, material composition, and characteristics of the fiber raw materials, and the manufacturing conditions and environment in the fiber manufacturing process. In consideration of such variations and the like, it is assumed that they are equal if they are within a range of some difference, for example, plus or minus 10% of the average value.

  The first cores 31, 31,... And the second cores 32, 32,... Can set the above dispersion parameters by adjusting the relative refractive index difference and the core diameter of the cores 31, 32. it can. For example, when the core diameter is reduced, the dispersion parameter can take a negative value.

  In addition, the first cores 31, 31,... And the second cores 32, 32,... Have opposite signs of the group velocity dispersion slopes and set the absolute values of the dispersion slopes equal. In order to set in this way, for example, the second cores 32, 32,... Are used as normal step-type cores, the dispersion slope is set to +, and the cladding around the first cores 31, 31,. By making the inner refractive index lower than the outer side, the sign of the dispersion slope is made negative. The fact that the absolute values of the group velocity dispersion slopes are equal does not mean that they are mathematically strict, but the variations in the structure, material composition, and characteristics of the fiber raw materials and the manufacturing conditions in the fiber manufacturing process. -Considering variations in the environment, etc., some differences, for example, within the range of plus or minus 20% of the average value, shall be equal.

  Examples of a method for manufacturing such a multi-core fiber 10 include a method in which a core rod is inserted into a quartz porous pipe and used as a base material, and a method in which a core rod and a quartz rod are packed into a quartz single hole pipe to form a base material. Can do.

  The first cores 31, 31,... And the second cores 32, 32,... Of the multi-core fiber 10 of the present embodiment are arranged in a regular dodecagon as described above. Therefore, when the multi-core fiber 10 of the present embodiment is rotated by 60 ° with the fiber central axis as the rotation axis, the first cores 31, 31,... Are in positions where the second cores 32, 32,. Conversely, the second cores 32, 32,... Move to the positions where the first cores 31, 31,. That is, the position of the first cores 31, 31,... And the position of the second cores 32, 32,.

  Therefore, when connecting the end surfaces of the two multi-core fibers 10 of the present embodiment, the first cores 31, 31,... The second cores 32, 32,... Of the one fiber 10 are in contact with the second cores 32, 32,. , ... are abutted against each other. In this way, in all the cores of the two multi-core fibers 10, the first core 31 can be connected to the second core 32, and the second core 32 can be connected to the first core 31.

  Assuming that the two multi-core fibers 10 connected here have the same length, the first cores 31, 31,... And the second cores 32, 32,. Since the absolute values of the parameters are equal and the signs are reversed, dispersion compensation is completely performed in all the cores. That is, the optical signal incident on the two connected multi-core fibers 10 is emitted in a state where there is no group velocity dispersion. Further, as described above, the first cores 31, 31,... And the second cores 32, 32,. Even when performed, dispersion compensation is performed at all wavelengths.

  When a plurality of multi-core fibers 10 of this embodiment are used and connected as described above to form an optical transmission line, dispersion compensation is performed for all the cores as in the case of the two multi-core fibers 10 described above. Even when wavelength division multiplexing communication is performed, dispersion compensation is performed at all wavelengths. In this case, it is preferable that the first cores 31, 31,... And the second cores 32, 32,... Have the same length in all the cores from the input end to the output end of the optical transmission line. . If a plurality of multi-core fibers 10 of this embodiment are used, such an optical transmission line can be formed by a simple method of simply rotating around the fiber center axis and connecting. That is, in an optical transmission line using a multi-core fiber, dispersion compensation can be performed for all cores simply and at low cost by using only one type of fiber. There is no need to use a different type of dispersion compensating fiber for dispersion compensation.

(Embodiment 2)
The multi-core fiber according to the second embodiment differs from the first embodiment in the arrangement of the cores, and is otherwise the same as the first embodiment. Hereinafter, the same points as those of the first embodiment will be omitted, but the description of the first embodiment also applies to the present embodiment as it is. The same applies to the optical transmission line.

  As shown in FIG. 2, the multi-core fiber 11 of the present embodiment includes three first cores 31, 31, 31 and three second cores 32, 32, 32 in a clad 21 made of quartz. There are a total of 6 cores. The six first cores 31, 31, 31 and the second cores 32, 32, 32 are arranged at each vertex of the regular hexagon in the fiber cross section. The first cores 31, 31, 31 and the second cores 32, 32, 32 are alternately arranged to form a regular hexagon. With this configuration, as in the first embodiment, when the multi-core fiber 11 is rotated by 60 ° around the fiber central axis, the positions of the first cores 31, 31, 31 and the positions of the second cores 32, 32, 32 are obtained. Is reversed.

  In the present embodiment, unlike the first embodiment, adjacent and adjacent cores are different types of cores. That is, the core adjacent to and close to the first core 31 is the second core 32, and the core adjacent to and close to the second core 32 is the first core 31. With such a configuration, the multi-core fiber 11 of this embodiment and the optical transmission line using the same exhibit all the effects of the first embodiment compared to the multi-core fiber 10 and the optical transmission line according to the first embodiment. In addition, there is an effect that crosstalk can be further suppressed. Hereinafter, the effect of suppressing crosstalk will be described.

  In a multi-core fiber, since a plurality of cores are contained in an optical fiber having the same diameter as that of a single-core fiber, there is a problem that a distance between adjacent cores is short and crosstalk occurs in these cores. In order to suppress crosstalk, the distance between the cores should be increased. However, this increases the diameter of the optical fiber itself, which makes it impossible to apply to existing communication devices and equipment. The cost of manufacturing communication devices and equipment becomes enormous.

  As another method for suppressing the crosstalk, it has been studied to provide a difference between the propagation constants of two adjacent cores (see, for example, Non-Patent Document 2).

  Here, the inventors of the present application have found that there is a large difference in propagation constant between the first core 31 and the second core 32 in the first embodiment. That is, since the sign of the dispersion parameter is positive and negative between the first core 31 and the second core 32, there is a large difference in the propagation constant. Based on this finding, when the first core 31 and the second core 32 are arranged adjacent to each other, it is possible to suppress the crosstalk, and the multicore fiber 11 of the present embodiment is manufactured. It was confirmed that it was greatly suppressed.

  In the multi-core fiber 11 of this embodiment and an optical transmission line connecting a plurality of the same, dispersion compensation can be performed for all cores as easily and at a low cost as in the first embodiment. Dispersion compensation is performed at the wavelength. Furthermore, crosstalk between the cores is sufficiently suppressed. All these effects can be achieved by using only one type of multi-core fiber 11.

-Modification 1-
Furthermore, the multi-core fiber 14 which concerns on the modification 1 which has arrange | positioned the marker (position display member) 41 in the clad 24 is shown in FIG. Note that the marker shape is painted black to make it stand out in the figure, but it is not actually black.

  In this modification, three markers 41, 41, 41 indicating the arrangement of the first cores 31, 31, 31 are arranged. The shapes of the markers 41, 41, 41 are substantially isosceles triangles, and the corners sandwiched between two equal sides indicate the first cores 31, 31, 31. The markers 41, 41, 41 are preferably those that do not affect the optical characteristics of the cores 31, 32 and are clearly visible. For example, a material having a refractive index greatly different from that of the clad 24 can be used.

  In this modification, since the core does not exist in the fiber central axis, markers 41, 41, and 41 are placed in the vicinity of the fiber central axis. Since the angle between the two equal sides of the markers 41, 41, 41 faces the outside of the fiber, and the side opposite to this angle is placed on the fiber center axis side, the markers 41, 41, 41 are located at the fiber center. It is an isosceles triangle from the axis toward the first core 31, 31, 31. In other words, in the multi-core fiber 14 in which the first core 31 and the second core 32 are alternately arranged at each vertex of the regular hexagon in the fiber cross section, the fiber center axis and the first core 31 are arranged. The marker 41 is arranged on a line connecting the two, and the marker 41 has a shape extending on the line, and points to the first core 31 when viewed from the fiber central axis.

  In this modification, there are markers 41, 41, and 41 indicating the three first cores 31, 31, and 31, respectively, and the marker shape is also a shape that clearly indicates the position of the core, so two multi-cores are provided. When connecting the fibers 14, the multi-core fibers 14 can be easily aligned in a short time. The marker 41 may be formed so as to show the second core 32 instead of the first core 31.

-Modification 2-
As shown in FIG. 4, the multi-core fiber 16 according to the second modification has only one marker 42 unlike the first modification. The marker 42 is formed in the clad 26 near the middle between one first core 42 and the fiber central axis. When the two multi-core fibers 16 are connected, if the end faces of the multi-core fibers 16 are positioned so that both the markers 42 are in point-symmetric positions with the center axis of the fiber as the center of symmetry, the first of the two fibers is connected. One core 31 is connected to the second core 32, and the second core 32 is connected to the first core 31. Thus, the presence of the marker 42 allows easy alignment in a short time when the fibers are connected. In the present modification, the marker 42 may be made of a material having a refractive index significantly different from that of the clad 26, or may be an air hole. The marker 42 may be formed so as to indicate the second core 32 instead of the first core 31.

(Embodiment 3)
The multi-core fiber according to the third embodiment is different from the second embodiment in the number and arrangement of cores, and the other points are the same as those in the second embodiment. In the following, the same points as in the second embodiment are omitted, but the description of the second embodiment also applies to this embodiment as it is.

  As shown in FIG. 5, the multi-core fiber 12 of this embodiment includes eight first cores 33, 33,... And eight second cores 34, 34,. There are a total of 16 cores. The 16 first cores 33, 33,... And the second cores 34, 34,... Are arranged in a square grid in the fiber cross section. The first cores 33, 33,... And the second cores 34, 34,... Are alternately arranged to form a large square as a whole. With this configuration, when the multi-core fiber 12 is rotated 90 ° around the fiber center axis, the positions of the first cores 33, 33,... And the positions of the second cores 34, 34,. Due to such a structure, when connecting the two multi-core fibers 12 as in the first and second embodiments, it is possible to easily connect only different types of cores.

  Moreover, since the cores which adjoin and adjoin are different types of cores similarly to Embodiment 2, crosstalk can fully be suppressed. In addition, the multicore fiber of this embodiment and the optical transmission line using the same have the same effects as those of the second embodiment.

-Modification-
Further, FIG. 6 shows a multicore fiber 18 similar to the modification of the second embodiment in which a marker (position display member) 43 is disposed in the clad 28. Note that the marker shape is painted black to make it stand out in the figure, but it is not actually black.

  In this modification, two markers 43, 43 indicating the arrangement of the four first cores 33, 33,... Arranged on one diameter of the multi-core fiber 18 are arranged. The markers 43, 43 are formed closer to the fiber side wall than the first cores 33, 33,. It is preferable that the markers 43 and 43 do not affect the optical characteristics of the cores 33 and 34 and are clearly visible. For example, a material or air hole having a refractive index greatly different from that of the clad 28 can be used.

  When the two multi-core fibers 18 are connected, if the end faces of the multi-core fibers 18 are positioned so that the lines connecting the two markers 43 and 43 in each fiber are orthogonal to each other, the first core of both fibers 33 is connected to the second core 34, and the second core 34 is connected to the first core 33. Since the markers 43 and 43 are present in this manner, alignment at the time of connecting the fibers can be easily performed in a short time. The marker 43 may be formed so as to indicate the second core 34 instead of the first core 33.

(Other embodiments)
The above embodiments and modifications are examples of the present invention, and the present invention is not limited to these examples. The arrangement of the cores may be any shape such as a regular octagon or a circle as a whole, and the number of cores may be at least one each of the first core and the second core.

  The absolute values of the dispersion parameters of the first core and the second core may not be equal. The absolute values of the group velocity dispersion slopes of the first core and the second core may not be equal.

  In the above embodiment, the core is not disposed on the fiber central axis, but the core may be disposed on the fiber central axis. If the core of the central axis portion is used differently from other cores, for example, for maintenance use, it is not necessary to perform dispersion compensation.

  As described above, the optical transmission line according to the present invention is useful as an optical communication transmission line because dispersion compensation is performed in each of a plurality of cores.

DESCRIPTION OF SYMBOLS 10 Multi-core fiber 11 Multi-core fiber 12 Multi-core fiber 14 Multi-core fiber 16 Multi-core fiber 18 Multi-core fiber 20 Cladding 21 Cladding 22 Cladding 24 Cladding 26 Cladding 28 Cladding 31 and 33 First core 32 and 34 Second core 41 Marker (position display member) )
42 Marker (position display member)
43 Marker (position display member)

Claims (6)

An optical transmission line formed by connecting a plurality of multi-core fibers each having a cladding and a plurality of cores,
The plurality of cores includes a first core whose group velocity dispersion is normal dispersion and a second core whose group velocity dispersion is anomalous dispersion,
The second core is disposed at a rotationally symmetric position of the first core with a fiber central axis as a rotation axis,
The multi-core fibers are optical transmission lines in which the first core and the second core are in contact with each other on the connection surface.   In the multi-core fiber, the second core is adjacent to and close to the first core, and the first core is adjacent to and close to the second core. The optical transmission line according to claim 1, wherein   The optical transmission line according to claim 2, wherein the absolute value of the group velocity dispersion of the first core and the absolute value of the group velocity dispersion of the second core are equal.   4. The optical transmission line according to claim 3, wherein a length of the first core and a length of the second core through which one optical signal passes from the input end to the output end are substantially the same.   The optical transmission line according to claim 4, wherein the group velocity dispersion slope of the first core and the group velocity dispersion slope of the second core have different signs.   6. The optical transmission line according to claim 2, further comprising a position display member that indicates an arrangement position of one of the first core and the second core. 7.

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